Grinding device

Abstract

To reduce grinding time in a creep-feed grinding process.SOLUTION: In a creep-feed grinding process, a creep-feed grinding control part 12 turns off an air bearing, and thereby a chuck table 20 including a spindle 25 and a casing 27 come in surface contact with each other. Therefore, the chuck table 20 is prevented from inclining even if force in a direction inclining a table rotary shaft 301 is applied to the chuck table 20 from a grinding grindstone 77, when the chuck table 20 is horizontally ground and fed toward the grinding grindstone 77. Accordingly, it is made possible to increase a grinding / feeding speed of the chuck table 20. As a result, grinding time in the creed-feed grinding process can be reduced.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a grinding apparatus. [Background Art]

[0002] As disclosed in Patent Document 1, there is a grinding apparatus capable of in-feed grinding and creep-feed grinding using an annular grinding wheel. This grinding apparatus includes: a rotation mechanism that rotates a chuck table holding a wafer; a moving mechanism that relatively moves the chuck table and the grinding wheel in a direction parallel to a holding surface; and a vertical moving mechanism that relatively moves the chuck table and the grinding wheel in a direction perpendicular to the holding surface.

[0003] In such a grinding apparatus, for example, during in-feed grinding, the chuck table is rotated and the grinding wheel is lowered in the vertical direction. On the other hand, during creep-feed grinding, the rotation of the chuck table is stopped, the grinding wheel is positioned below the upper surface of the wafer, and the chuck table is moved in the horizontal direction. [Prior Art Literature] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2010-016181 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2008-246628 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] In the grinding apparatus as described above, the rotation mechanism that rotates the chuck table includes: a table base on which the chuck table is placed; a spindle coupled to the table base; and a casing that rotatably supports the spindle via a bearing. As disclosed in Patent Document 2, an air bearing formed by supplying air, or a ball bearing is used for the bearing.

[0006] During creep-feed grinding, the lower surface of the grinding wheel is positioned below the upper surface of the wafer, on the outside of the wafer. The chuck table and the grinding wheel are then moved relative to each other in a direction parallel to the holding surface. This causes the grinding wheel to move from one outer edge of the wafer towards the center, and then towards the other outer edge, grinding the wafer. At this time, a force is applied to the chuck table that tilts its axis of rotation.

[0007] The force that tilts the axis of rotation is also applied to the bearings, which can cause them to break. Furthermore, in creep-feed grinding, the force that tilts the axis of rotation due to the contact of the rotating grinding wheel with the wafer, and the force that tilts the axis of rotation in the direction of movement due to the relative movement of the chuck table and grinding wheel parallel to the holding surface, are both applied to the bearings. This makes it difficult to increase the speed at which the chuck table and grinding wheel move relative to the holding surface parallel to the holding surface. As a result, the processing time becomes longer.

[0008] Therefore, the object of the present invention is to shorten the grinding time for creep feed grinding in a grinding apparatus capable of performing both infeed grinding and creep feed grinding. [Means for solving the problem]

[0009] The grinding apparatus of the present invention (this grinding apparatus) is a grinding apparatus for grinding a workpiece with an annular grinding wheel, comprising: a chuck table that holds the workpiece by a holding surface; a support mechanism that rotatably supports the chuck table; a grinding mechanism that rotates an annular grinding wheel to grind the workpiece; a horizontal movement mechanism that moves either the chuck table or the grinding mechanism relative to the other in a direction parallel to the holding surface; a vertical movement mechanism that moves either the chuck table or the grinding mechanism relative to the other in a direction perpendicular to the holding surface; and a control unit, wherein the support mechanism supports the chuck table via an air bearing. The horizontal movement mechanism comprises a casing capable of moving and a motor for rotating the chuck table, the horizontal movement mechanism includes a Y-axis encoder for detecting the position of the chuck table relative to the grinding mechanism in a direction parallel to the holding surface, and the vertical movement mechanism includes a Z-axis encoder for detecting the position of the grinding mechanism relative to the chuck table in a direction perpendicular to the holding surface, and the control unit, when performing infeed grinding to grind a workpiece by rotating the chuck table, turns on the air bearing to rotate the chuck table and uses the horizontal movement mechanism to position the grinding wheel so that it passes through the center of the workpiece held on the holding surface. The grinding mechanism is controlled to rotate the grinding wheel, An infeed grinding control unit that uses the vertical movement mechanism to move either the chuck table or the grinding mechanism toward the other, and grinds the workpiece with the grinding wheel, and when performing creep feed grinding which grinds the workpiece without rotating the chuck table, the air bearing is turned OFF and the chuck table is not rotated, and the vertical movement mechanism is used to position the lower surface of the grinding wheel below the upper surface of the workpiece on the outside of the workpiece. The grinding mechanism is controlled to rotate the grinding wheel, The system includes a creep feed grinding control unit that uses the horizontal movement mechanism to move either the chuck table or the grinding mechanism horizontally relative to the other, thereby grinding the workpiece with the grinding wheel. The grinding apparatus may include a holding surface height measuring device for measuring the height of the holding surface; a storage unit for storing either the height position of the grinding mechanism when the lower surface of the grinding wheel is in contact with the holding surface when the air bearing is turned ON, or the height position of the grinding mechanism when the lower surface of the grinding wheel is in contact with the holding surface when the air bearing is turned OFF; and a height position calculation unit for calculating the height position of the grinding mechanism that is not stored in the storage unit, using the height position of the grinding mechanism stored in the storage unit and the difference between the height of the holding surface when the air bearing is turned ON and the height of the holding surface when the air bearing is turned OFF. [Effects of the Invention]

[0010] In this grinding apparatus, during creep feed grinding, the creep feed grinding control unit can ensure close contact between the chuck table and the casing by turning off the air bearing. Therefore, even when force is applied from the grinding wheel to the chuck table during horizontal grinding feed towards the grinding wheel, tilting of the chuck table can be suppressed. Consequently, the grinding feed speed of the chuck table can be increased. This allows for a reduction in grinding time during creep feed grinding.

[0011] Furthermore, this grinding apparatus uses a holding surface height measuring device to measure the origin height position of the grinding mechanism when either the air bearing is ON or OFF, thereby allowing the calculation of the origin height position of the grinding mechanism in the other state. Therefore, the setup time for the grinding mechanism can be reduced. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view showing the configuration of the grinding machine. [Figure 2] This is an explanatory diagram showing the configuration of the grinding device. [Figure 3] This is an explanatory diagram showing an air bearing. [Figure 4]It is an explanatory diagram showing an in-feed grinding step. [Figure 5] It is an explanatory diagram showing a creep feed grinding step. [Figure 6] It is an explanatory diagram showing a setup step. [Figure 7] It is an explanatory diagram showing a setup step.

Mode for Carrying Out the Invention

[0013] As shown in FIG. 1, the grinding apparatus 1 according to the present embodiment is an apparatus that grinds a wafer 100 as a workpiece by an annular grinding wheel. In particular, the grinding apparatus 1 is capable of performing in-feed grinding and creep feed grinding on the wafer 100.

[0014] The wafer 100 is, for example, a circular semiconductor wafer, and includes a front surface 101 and a back surface 102. The front surface 101 of the wafer 100 facing downward in FIG. 1 holds a plurality of devices and is protected by attaching a protective tape 103 thereto. The back surface 102 of the wafer 100 serves as a surface to be ground on which grinding processing is performed.

[0015] As shown in FIG. 1, the grinding apparatus 1 includes a rectangular parallelepiped base 2, a column 3 extending upward, and a control unit 7 that controls each member of the grinding apparatus 1.

[0016] An opening 5 is provided on the upper surface side of the base 2. A wafer holding mechanism 18 is disposed inside the opening 5. The wafer holding mechanism 18 includes a chuck table 20 that holds the wafer 100 by a holding surface 22, and a support mechanism 26 that rotatably supports the chuck table 20.

[0017] As shown in FIG. 2, the chuck table 20 includes a circular plate-shaped porous member 21 and a frame body 23 that supports the porous member 21. The porous member 21 can be communicated with a suction source not shown in the drawings. A suction force from the suction source is transmitted to a holding surface 22 which is an upper surface of the porous member 21, whereby the chuck table 20 can suck and hold a wafer 100 by the holding surface 22. A frame body surface 24 which is an upper surface of the frame body 23 is formed so as to be flush with the holding surface 22.

[0018] Further, the chuck table 20 includes a spindle 25 connected to a lower surface of the frame body 23. The spindle 25 extends in the Z-axis direction. A large-diameter first disk portion 251 is formed at an upper end of the spindle 25. A large-diameter second disk portion 252 is also formed at a lower end of the spindle 25. A small-diameter portion 253 having a relatively small diameter is provided between the first disk portion 251 and the second disk portion 252. The first disk portion 251 is connected to the lower surface of the frame body 23. Thereby, the chuck table 20 including the spindle 25 is configured to rotate integrally.

[0019] The support mechanism 26 rotatably supports the chuck table 20, and is configured to rotate the chuck table 20 around the center of the holding surface 22. As shown in FIG. 2, the support mechanism 26 includes a rotation mechanism 30 that rotates the spindle 25 of the chuck table 20.

[0020] The rotation mechanism 30 is, for example, a pulley mechanism, and includes a motor 31 serving as a driving source, a driving pulley 32 attached to a shaft of the motor 31, a driven pulley 34 connected to the driving pulley 32 via an endless belt 33, a rotating shaft 35 that supports the driven pulley 34 and is connected to the second disk portion 252 of the spindle 25, and a rotary joint 36 connected to the rotating shaft 35.

[0021] In the rotating mechanism 30, the motor 31 rotates the main pulley 32, causing the endless belt 33 to rotate as the main pulley 32 rotates. As the endless belt 33 rotates, the driven pulley 34 and the rotating shaft 35 rotate. As a result, the chuck table 20, including the spindle 25 connected to the rotating shaft 35, rotates around the table rotation axis 301, which passes through the center of the holding surface 22, as shown by arrow 601. Thus, in the rotating mechanism 30, the motor 31 rotates the spindle 25, thereby rotating the chuck table 20.

[0022] Furthermore, the rotating mechanism 30 includes a casing 27. The casing 27 is configured to rotatably support the spindle 25 of the chuck table 20 via an air bearing.

[0023] The casing 27 is an annular member and is positioned to fit between the first disc portion 251 and the second disc portion 252 of the spindle 25, and to form a small gap air bearing between the small diameter portion 253, the first disc portion 251 and the second disc portion 252 of the spindle 25 and the casing 27. The casing 27 is installed on the Y-axis moving table 45 of the horizontal moving mechanism 40, which will be described later, via a support column 28.

[0024] Furthermore, as shown in Figures 2 and 3, the casing 27 includes an air supply passage 82 and a plurality of air outlets 83 that extend into the casing 27. The air supply passage 82 is connected to an air supply source 80 via an air valve 81.

[0025] The air outlet 83 is provided in the casing 27 so as to face the small-diameter portion 253, the first disc portion 251, and the second disc portion 252 of the spindle 25, and is connected to the air supply passage 82.

[0026] In the support mechanism 26, when the air valve 81 is opened, air from the air supply source 80 is ejected from the air outlet 83 of the casing 27 toward the spindle 25, thereby forming an air bearing consisting of an air layer of a predetermined thickness.

[0027] In this embodiment, as shown in Figure 3, the air bearing includes a radial air bearing 85, which is a cylindrical air layer, and a first thrust air bearing 86 and a second thrust air bearing 87, which are annular plate-shaped air layers. The radial air bearing 85 is formed between the small diameter portion 253 of the spindle 25 and the casing 27, surrounding the small diameter portion 253. The first thrust air bearing 86 is formed between the first disc portion 251 of the spindle 25 and the casing 27. The second thrust air bearing 87 is formed between the second disc portion 252 of the spindle 25 and the casing 27.

[0028] Thus, when the air valve 81 is open and the air bearings 85-87 are formed (when the air bearings are ON), the casing 27 can support the chuck table 20, including the spindle 25, via the air bearings 85-87. In this embodiment, when the air valve 81 is closed and the air bearings 85-87 are not formed (air bearing OFF), the casing 27 supports the chuck table 20 by supporting the spindle 25 in surface contact without using air bearings.

[0029] Furthermore, as shown in Figure 1, a cover plate 39 is provided around the chuck table 20, which moves along the Y-axis direction together with the chuck table 20. A bellows cover 4 that expands and contracts in the Y-axis direction is connected to the cover plate 39. Below the wafer holding mechanism 18, a horizontal movement mechanism 40 is provided.

[0030] The horizontal movement mechanism 40 moves the chuck table 20 and the grinding mechanism 70 relative to each other in the Y-axis direction, which is parallel to the holding surface 22. In this embodiment, the horizontal movement mechanism 40 is configured to move the wafer holding mechanism 18, including the chuck table 20, in the Y-axis direction relative to the grinding mechanism 70.

[0031] The horizontal movement mechanism 40 includes a pair of Y-axis guide rails 42 parallel to the Y-axis direction, a Y-axis movement table 45 that slides on the Y-axis guide rails 42, a Y-axis ball screw 43 parallel to the Y-axis guide rails 42, a Y-axis motor 44 connected to the Y-axis ball screw 43, a Y-axis encoder 46 for detecting the rotation angle of the Y-axis motor 44, and a holder 41 for holding these components.

[0032] The Y-axis moving table 45 is slidably mounted on the Y-axis guide rail 42 via a sliding member 451 (see Figure 2). A nut portion 401 (see Figure 2) is provided on the underside of the Y-axis moving table 45. A Y-axis ball screw 43 is screwed into this nut portion 401. The Y-axis motor 44 is connected to one end of the Y-axis ball screw 43.

[0033] In the horizontal movement mechanism 40, the Y-axis motor 44 rotates the Y-axis ball screw 43, causing the Y-axis movement table 45 to move in the Y-axis direction along the Y-axis guide rail 42. The Y-axis movement table 45 is fitted with support columns 28 of the support mechanism 26 of the wafer holding mechanism 18. Therefore, as the Y-axis movement table 45 moves in the Y-axis direction, the wafer holding mechanism 18, including the chuck table 20, also moves in the Y-axis direction.

[0034] In this embodiment, the chuck table 20 is moved along the Y-axis direction by a horizontal movement mechanism 40 between a wafer placement area on the -Y direction side for placing the wafer 100 on the holding surface 22 and a grinding area on the +Y direction side where the wafer 100 is ground. Furthermore, the Y-axis encoder 46 of the horizontal movement mechanism 40 can recognize the position of the chuck table 20 in the Y-axis direction as it is moved by the horizontal movement mechanism 40 by detecting the rotation angle of the Y-axis motor 44.

[0035] Furthermore, as shown in Figure 1, a column 3 is erected on the base 2 in the +Y direction. A grinding mechanism 70 for grinding the wafer 100 and a vertical movement mechanism 50 are provided on the front surface of the column 3.

[0036] The vertical movement mechanism 50 moves the chuck table 20 and the grinding mechanism 70 relative to each other in the Z-axis direction (grinding feed direction), which is perpendicular to the holding surface 22. In this embodiment, the vertical movement mechanism 50 is configured to move the grinding mechanism 70 in the Z-axis direction relative to the wafer holding mechanism 18, which includes the chuck table 20.

[0037] The vertical movement mechanism 50 includes a pair of Z-axis guide rails 51 parallel to the Z-axis direction, a Z-axis movement table 53 that slides on the Z-axis guide rails 51, a Z-axis ball screw 52 parallel to the Z-axis guide rails 51, a Z-axis motor 54, a Z-axis encoder 55 for detecting the rotation angle of the Z-axis motor 54, and a holder 56 attached to the Z-axis movement table 53. The holder 56 holds the grinding mechanism 70.

[0038] The Z-axis moving table 53 is slidably mounted on the Z-axis guide rail 51 via a sliding member 531 (see Figure 2). The Z-axis moving table 53 is provided with a nut portion 501 (see Figure 2). A Z-axis ball screw 52 is screwed into this nut portion 501. The Z-axis motor 54 is connected to one end of the Z-axis ball screw 52.

[0039] In the vertical movement mechanism 50, the Z-axis motor 54 rotates the Z-axis ball screw 52, ​​causing the Z-axis moving table 53 to move in the Z-axis direction along the Z-axis guide rail 51. As a result, the holder 56 attached to the Z-axis moving table 53, and the grinding mechanism 70 held in the holder 56, move in the Z-axis direction together with the Z-axis moving table 53.

[0040] Furthermore, the Z-axis encoder 55 of the vertical movement mechanism 50 can detect the rotation angle of the Z-axis motor 54, thereby recognizing the height of the grinding mechanism 70 moved by the vertical movement mechanism 50 (for example, the height of the grinding wheel 77, which will be described later).

[0041] The grinding mechanism 70 is configured to grind a wafer by rotating an annular grinding wheel. As shown in Figure 1, the grinding mechanism 70 includes a spindle housing 71 fixed to a holder 56, a spindle 72 rotatably held in the spindle housing 71, a spindle motor 73 for rotationally driving the spindle 72, a wheel mount 74 attached to the lower end of the spindle 72, and a grinding wheel 75 supported by the wheel mount 74.

[0042] The spindle housing 71 is held by the holder 56. The spindle 72 is supported by the spindle housing 71 so as to extend along the Z-axis direction and be rotatable about an axis along the direction of extension.

[0043] The spindle motor 73 is connected to the upper end of the spindle 72 and rotates the spindle 72.

[0044] The wheel mount 74 is formed in a disc shape and is fixed to the lower end of the spindle 72. The wheel mount 74 supports the grinding wheel 75.

[0045] The grinding wheel 75 is formed such that its outer diameter is approximately the same as the outer diameter of the wheel mount 74. The grinding wheel 75 includes an annular wheel base 76 made of a metal material. As shown in Figure 2, a processing water channel 761 is formed inside the wheel base 76 for supplying processing water from a water source (not shown) to the grinding wheel 77.

[0046] As shown in Figure 1, an annular grinding wheel 77, consisting of multiple grinding wheels arranged in an annular pattern around its entire circumference, is fixed to the lower surface of the wheel base 76.

[0047] This annular grinding wheel 77 is formed on the wheel base 76 such that the extension direction of the spindle 72 passes through its center. Therefore, the grinding wheel 77 is rotated by the spindle motor 73, as shown by arrow 602, via the spindle 72, wheel mount 74, and wheel base 76, around the grinding wheel rotation axis 701 (see Figure 2) passing through its center, to grind the wafer 100 held on the chuck table 20 located in the grinding area.

[0048] In this manner, the grinding mechanism 70 grinds the wafer 100 held on the holding surface 22 of the chuck table 20 by rotating the grinding wheel 77 around a grinding wheel rotation axis 701 that passes through the center of the annular grinding wheel 77.

[0049] Furthermore, as shown in Figure 1, a measuring mechanism 60 is provided on the side of the opening 5 in the base 2. The measuring mechanism 60 can measure the height of the holding surface 22 and the height of the wafer 100 by contact.

[0050] In other words, the measuring mechanism 60 brings the holding surface height measuring instrument 61 and the wafer height measuring instrument 62, which are measuring probes, into contact with the frame surface 24 of the chuck table 20 and the wafer 100, respectively.

[0051] This allows the measuring mechanism 60 to measure the height of the holding surface 22 of the chuck table 20, which is flush with the frame surface 24, and the height of the wafer 100. Furthermore, the measuring mechanism 60 can also calculate the thickness of the wafer 100 based on the difference between the measured height of the holding surface 22 and the height of the wafer 100.

[0052] The holding surface height measuring instrument 61 and the wafer height measuring instrument 62 may be non-contact distance measuring instruments that use light or sound waves reflected from the frame surface 24 and the upper surface of the wafer 100, respectively.

[0053] Furthermore, the control unit 7 includes a CPU that performs calculations according to a control program, and a storage medium such as memory. The control unit 7 controls each of the above-mentioned components of the grinding apparatus 1 to perform grinding on the wafer 100. As shown in Figure 1, the control unit 7 includes an infeed grinding control unit 11, a creep feed grinding control unit 12, a storage unit 13, and a height position calculation unit 14.

[0054] The operation of the grinding device 1 controlled by the control unit 7 and its components will be described below.

[0055] [Infeed grinding process] This process is performed when the wafer 100 is infeed ground by the grinding device 1.

[0056] In this process, first, the wafer 100 is held on the holding surface 22 of the chuck table 20 of the wafer holding mechanism 18 located in the wafer mounting area, with the back surface 102 facing upwards.

[0057] Subsequently, the infeed grinding control unit 11 of the control unit 7 turns on the air bearings. That is, as shown in Figure 4, the infeed grinding control unit 11 opens the air valve 81 and blows air from the air supply source 80 from the air outlet 83 of the casing 27 toward the spindle 25 of the chuck table 20, thereby forming air bearings 85-87.

[0058] Next, the infeed grinding control unit 11 controls the motor 31 (see Figure 2) of the rotation mechanism 30 to rotate the chuck table 20 around the table rotation axis 301 that passes through the center of the holding surface 22, as shown by the arrow 601.

[0059] Furthermore, the infeed grinding control unit 11 controls the horizontal movement mechanism 40 to move the wafer holding mechanism 18, including the chuck table 20, to the grinding area on the +Y direction side. Then, as shown in Figure 4, the infeed grinding control unit 11 positions the grinding wheel 77 of the grinding mechanism 70 above the wafer 100 so that the grinding wheel 77 passes through the center of the wafer 100 held on the holding surface 22.

[0060] Furthermore, the infeed grinding control unit 11 controls the spindle motor 73 (see Figure 1) of the grinding mechanism 70 to rotate the spindle 72, thereby rotating the grinding wheel 77 around its grinding wheel rotation axis 701 as shown by the arrow 602, as shown in Figure 4.

[0061] Next, the infeed grinding control unit 11 controls the vertical movement mechanism 50 to move the grinding mechanism 70 and the chuck table 20 in a direction that brings them relatively closer together. In this embodiment, the infeed grinding control unit 11 feeds the grinding mechanism 70, including the grinding wheel 77, in a direction that approaches the chuck table 20 perpendicularly. In this way, the infeed grinding control unit 11 grinds the back surface 102 of the wafer 100 held on the holding surface 22 of the chuck table 20 with the lower surface of the grinding wheel 77.

[0062] During this grinding process, the infeed grinding control unit 11 measures the thickness of the wafer 100 being ground using a measuring mechanism 60 that includes a holding surface height measuring device 61 and a wafer height measuring device 62. The infeed grinding control unit 11 then confirms that the measured thickness of the wafer 100 has reached a preset target thickness and terminates the infeed grinding.

[0063] In this manner, the infeed grinding control unit 11 turns on the air bearing to rotate the chuck table 20, positions the grinding wheel 77 so that it passes through the center of the wafer 100 held on the holding surface 22, moves the grinding mechanism 70 toward the chuck table 20, and grinds the wafer 100 with the grinding wheel 77.

[0064] [Creep Feed Grinding Process] This process is performed when the wafer 100 is subjected to creep-feed grinding by the grinding device 1.

[0065] In this process as well, first, the wafer 100 is held on the holding surface 22 of the chuck table 20 of the wafer holding mechanism 18 located in the wafer mounting area, with the back surface 102 facing upwards.

[0066] Subsequently, the creep feed grinding control unit 12 of the control unit 7 turns off the air bearing, as shown in Figure 5. That is, the creep feed grinding control unit 12 closes the air valve 81, stopping the ejection of air from the air outlet 83 of the casing 27 toward the spindle 25 of the chuck table 20. As a result, air bearings 85-87 are not formed. Therefore, the first thrust air bearing 86 shown in Figure 4 is not formed, and as shown in Figure 5, the lower surface of the first disc portion 251 of the spindle 25 contacts the upper surface of the casing 27, and the spindle 25 is placed directly on the casing 27. In other words, the chuck table 20 including the spindle 25 and the casing 27 are in close contact with each other through surface contact.

[0067] Furthermore, as shown in Figure 5, the creep feed grinding control unit 12 positions the lower surface of the grinding wheel 77 outside the wafer 100 and lower than the back surface 102 of the wafer 100, which is the surface to be ground.

[0068] Specifically, first, the creep feed grinding control unit 12 controls the horizontal movement mechanism 40 to position the wafer holding mechanism 18, including the chuck table 20, at the creep feed grinding start position. The creep feed grinding start position is, for example, the position furthest to the -Y direction in the grinding area, and is a position where the grinding wheel 77 does not come into contact with the wafer 100 held by the chuck table 20, as shown in Figure 5. At this time, the lower surface of the grinding wheel 77 is located horizontally outward from the outer circumference of the wafer 100 and the outer circumference of the holding surface 22.

[0069] Next, the creep feed grinding control unit 12 determines the height position of the lower surface of the grinding wheel 77 (grinding height position) such that the wafer 100 after creep feed grinding has a predetermined thickness. This grinding height position is lower than the back surface 102 of the wafer 100 before creep feed grinding. For example, the creep feed grinding control unit 12 determines the grinding height position from a preset target thickness of the wafer 100 after creep feed grinding and a previously acquired height of the holding surface 22.

[0070] Subsequently, the creep feed grinding control unit 12 uses the vertical movement mechanism 50 to move the grinding mechanism 70, including the grinding wheel 77, downward, setting the height of the lower surface of the grinding wheel 77 to the aforementioned grinding height position.

[0071] In this process, the creep feed grinding control unit 12 controls a grinding wheel rotation axis adjustment mechanism (not shown) to tilt the grinding wheel rotation axis 701 of the grinding wheel 77 relative to the holding surface 22 of the chuck table 20 slightly toward the direction of movement rather than perpendicular to the direction of relative movement between the wafer 100 and the grinding wheel 77 in the creep feed grinding process (direction of arrow 611), as shown in Figure 5. As a result, the grinding wheel 77 is tilted relative to the chuck table 20 with respect to the direction of movement (Y-axis direction).

[0072] Furthermore, the creep feed grinding control unit 12 controls the spindle motor 73 (see Figure 1) of the grinding mechanism 70 to rotate the spindle 72, thereby rotating the grinding wheel 77 around its grinding wheel rotation axis 701 as shown by the arrow 602.

[0073] The creep feed grinding control unit 12 then moves the wafer 100 and the grinding wheel 77 relative to each other in a direction parallel to the holding surface 22. In this embodiment, the creep feed grinding control unit 12 uses the horizontal movement mechanism 40 to horizontally feed the wafer holding mechanism 18, which includes the chuck table 20 holding the wafer 100, towards the grinding wheel 77 along the Y-axis, as shown by the arrow 611 in Figure 5. In this way, the creep feed grinding control unit 12 grinds the back surface 102 of the wafer 100 with the side surface of the rotating grinding wheel 77. As a result, the back surface 102 is removed by a predetermined amount of creep feed grinding.

[0074] During this grinding process, the creep feed grinding control unit 12 may measure the thickness of the wafer 100 being ground using a measuring mechanism 60 that includes a holding surface height measuring device 61 and a wafer height measuring device 62. In this case, the creep feed grinding control unit 12 may terminate the creep feed grinding after confirming that the measured thickness of the wafer 100 has reached the target thickness. Alternatively, if the measured thickness of the wafer 100 has not reached the target thickness, the creep feed grinding control unit 12 may perform creep feed grinding again.

[0075] In this manner, the creep feed grinding control unit 12 turns off the air bearing and does not rotate the chuck table 20, positions the lower surface of the grinding wheel 77 below the back surface 102, which is the upper surface of the wafer 100, on the outside of the wafer 100, moves the chuck table 20 horizontally relative to the grinding mechanism 70, and grinds the wafer 100.

[0076] As described above, in this embodiment, during the creep feed grinding process, the creep feed grinding control unit 12 turns off the air bearing, thereby bringing the chuck table 20, including the spindle 25, and the casing 27 into surface contact and making them tightly attached to each other. Therefore, when the chuck table 20 is fed horizontally toward the grinding wheel 77 for grinding, even if a force is applied from the grinding wheel 77 to the chuck table 20 in a direction that tilts the table rotation axis 301, the tilting of the chuck table 20 can be suppressed. Consequently, the grinding feed speed of the chuck table 20 can be increased. Therefore, the grinding time in the creep feed grinding process can be shortened.

[0077] The control unit 7 may also perform the following setup steps to determine the origin height of the grinding mechanism 70 prior to the infeed grinding step and creep feed grinding step described above. The origin height of the grinding mechanism 70 is the height of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 of the chuck table 20.

[0078] [Setup Process] In this process, the control unit 7 first turns on the air bearings, as shown in Figure 6. That is, the control unit 7 opens the air valve 81 and blows air from the air supply source 80 from the air outlet 83 of the casing 27 toward the spindle 25 of the chuck table 20, thereby forming air bearings 85-87.

[0079] In this state, the control unit 7 uses the vertical movement mechanism 50 to lower the grinding mechanism 70 so that the lower surface of the grinding wheel 77 comes into contact with the holding surface 22 of the chuck table 20, which is not holding the wafer 100. Furthermore, the control unit 7 obtains the height of the grinding mechanism 70 when the lower surface of the grinding wheel 77 comes into contact with the holding surface 22 using the Z-axis encoder 55 of the vertical movement mechanism 50 (see Figure 1).

[0080] In this way, the control unit 7 acquires the first origin height position Z1 of the grinding mechanism 70 when the air bearing is turned ON, that is, the height position of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 when the air bearing is turned ON. The control unit 7 stores the acquired first origin height position Z1 in the storage unit 13.

[0081] Furthermore, at this time, the control unit 7 brings the holding surface height measuring instrument 61 of the measuring mechanism 60 into contact with the frame surface 24 of the chuck table 20 to measure the first holding surface height H1, which is the height of the holding surface 22 when the air bearing is ON, and stores this first holding surface height H1 in the storage unit 13.

[0082] Next, the control unit 7 turns off the air bearing, as shown in Figure 7. That is, the control unit 7 closes the air valve 81, stopping the ejection of air from the air outlet 83 of the casing 27 toward the spindle 25. As a result, air bearings 85-87 are not formed. Therefore, the first thrust air bearing 86 is not formed, and as shown in Figure 7, the lower surface of the first disc portion 251 of the spindle 25 contacts the upper surface of the casing 27, and the spindle 25 is placed directly on the casing 27.

[0083] In this state, the control unit 7 brings the holding surface height measuring instrument 61 of the measuring mechanism 60 into contact with the frame surface 24 of the chuck table 20 to measure the second holding surface height H2, which is the height of the holding surface 22 when the air bearing is OFF, and stores this second holding surface height H2 in the storage unit 13.

[0084] Subsequently, the height position calculation unit 14 of the control unit 7 determines the air gap (H1-H2), which is the difference between the first holding surface height H1 and the second holding surface height H2. This air gap (H1-H2) corresponds to the spacing (gap spacing) of the first thrust air bearing 86 when the air bearing is ON. Furthermore, the height position calculation unit 14 subtracts the above-mentioned air gap (H1-H2) from the first origin height position Z1 of the grinding mechanism 70 stored in the memory unit 13 to determine the origin height position of the grinding mechanism 70 when the air bearing is OFF, that is, the second origin height position Z2, which is the height of the grinding mechanism 70 when the lower surface of the grinding wheel 77 contacts the holding surface 22 when the air bearing is OFF, and stores this second origin height position Z2 in the memory unit 13.

[0085] In this way, the first origin height position Z1, which is the origin height of the grinding mechanism 70 when the air bearing is ON, and the second origin height position Z2, which is the origin height of the grinding mechanism 70 when the air bearing is OFF, are determined. In this process, when determining the second origin height position Z2, it is not necessary to lower the grinding mechanism 70 and bring the lower surface of the grinding wheel 77 into contact with the holding surface 22, so the time required to determine the second origin height position Z2 can be shortened.

[0086] In the above explanation, the second origin height position Z2 of the grinding mechanism 70 when the air bearing is OFF is determined based on the first origin height position Z1 of the grinding mechanism 70 when the air bearing is ON. However, the first origin height position Z1 may be determined based on the second origin height position Z2.

[0087] In this case, when the air bearing is ON, the control unit 7 uses the holding surface height measuring instrument 61 of the measuring mechanism 60 to acquire only the first holding surface height H1 of the holding surface 22 of the chuck table 20. On the other hand, when the air bearing is OFF, in addition to the second holding surface height H2 of the holding surface 22 at that time, the control unit 7 acquires the second origin height position Z2 of the grinding mechanism 70. That is, the control unit 7 uses the vertical movement mechanism 50 to lower the grinding mechanism 70 so that the lower surface of the grinding wheel 77 comes into contact with the holding surface 22 of the chuck table 20, and acquires the second origin height position Z2, which is the height of the grinding mechanism 70 at that time, using the Z-axis encoder 55 and stores it in the storage unit 13.

[0088] Then, the height position calculation unit 14 adds the air gap (H1-H2), which is the difference between the first holding surface height H1 and the second holding surface height H2, to the second origin height position Z2 of the grinding mechanism 70 stored in the memory unit 13, thereby determining the first origin height position Z1 of the grinding mechanism 70 when the air bearing is ON, and stores this first origin height position Z1 in the memory unit 13.

[0089] Thus, in this embodiment, the memory unit 13 stores either the first origin height position Z1, which is the height position of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 when the air bearing is ON, or the second origin height position Z2, which is the height position of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 when the air bearing is OFF. The height position calculation unit 14 then uses the origin height position of the grinding mechanism 70 stored in the memory unit 13, and the difference between the first holding surface height H1 when the air bearing is ON and the second holding surface height H2 when the air bearing is OFF, to calculate the origin height position of the grinding mechanism 70 that is not stored in the memory unit 13.

[0090] According to this method, by measuring the origin height position of the grinding mechanism 70 when the air bearing is ON or OFF, the origin height position of the grinding mechanism 70 in the other state can be calculated. Therefore, the time required to acquire (set up) the origin height position of the grinding mechanism 70 can be reduced.

[0091] Alternatively, the height H1 of the first holding surface when the air bearing is ON and the height H2 of the second holding surface when the air bearing is OFF may be measured based on the height (origin height) of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 of the chuck table 20.

[0092] Furthermore, when measuring the height of the holding surface 22 of the chuck table 20 based on the origin height, which is the height of the grinding mechanism 70 when the lower surface of the grinding wheel 77 is in contact with the holding surface 22 of the chuck table 20, a contact-type sensor that can be placed between the lower surface of the grinding wheel 77 and the holding surface 22 may be used. When using this sensor, the grinding wheel 77 is lowered so that its lower surface comes into contact with the upper end of the sensor. Then, by lowering the grinding wheel 77 further, the lower end of the sensor comes into contact with the holding surface 22, and the sensor turns ON. The origin height of the grinding mechanism 70 may be determined by subtracting the length of the sensor in the Z-axis direction (distance between the upper and lower ends), which has been recognized in advance, from the height of the grinding mechanism 70 at this time. Alternatively, the sensor may be a load sensor. [Explanation of Symbols]

[0093] 1: Grinding device, 2: Base, 3: Column, 4: Bellows cover, 5: Opening, 7: Control unit, 11: Infeed grinding control unit, 12: Creep feed grinding control unit, 13: Memory unit, 14: Height position calculation unit, 18: Wafer holding mechanism, 20: Chuck table, 21: Porous member, 22: Holding surface, 23: Frame, 24: Frame surface, 25: Spindle, 26: Support mechanism, 27: Casing, 28: Support column, 30: Rotating mechanism, 31: Motor, 32: Drive pulley, 33: Endless belt, 34: Driven pulley, 35: Rotating shaft, 36: Rotary joint, 39: Cover plate, 40: Horizontal movement mechanism, 41: Holding base, 42: Y-axis guide rail, 43: Y-axis ball screw, 44: Y-axis motor, 45: Y-axis moving table, 46: Y-axis encoder, 50: Vertical movement mechanism, 51: Z-axis guide rail, 52: Z-axis ball screw, 53: Z-axis moving table, 54: Z-axis motor, 55: Z-axis encoder, 56: Holder, 60: Measuring mechanism, 61: Holding surface height measuring device, 62: Wafer height measuring device, 70: Grinding mechanism, 71: Spindle housing, 72: Spindle, 73: Spindle motor, 74: Wheel mount, 75: Grinding wheel, 76: Wheel base, 77: Grinding wheel, 80: Air supply source, 81: Air valve, 82: Air supply passage, 83: Air outlet, 85: Radial air bearing, 86: First thrust air bearing, 87: Second thrust air bearing, 100: Wafer, 101: Front surface, 102: Back surface, 103: Protective tape 251: First disc section, 252: Second disc section, 253: Small diameter section, 301: Table rotation axis, 401: Nut part, 451: Sliding member, 501: Nut part, 531: Sliding part, 601: Arrow, 602: Arrow, 611: Arrow, 701: Grinding wheel rotation axis, 761: Machining water channel, H1: Height of the first retaining surface, H2: Height of the second retaining surface, Z1: First origin height position, Z2: Second origin height position

Claims

1. A grinding device that grinds a workpiece with an annular grinding wheel, A chuck table that holds the workpiece with a holding surface, A support mechanism that rotatably supports the chuck table, A grinding mechanism that grinds the workpiece by rotating an annular grinding wheel, A horizontal movement mechanism that moves either the chuck table or the grinding mechanism relative to the other in a direction parallel to the holding surface, A vertical movement mechanism that moves either the chuck table or the grinding mechanism relative to the other in a direction perpendicular to the holding surface, It comprises a control unit and, The support mechanism comprises a casing capable of supporting the chuck table via air bearings, and a motor for rotating the chuck table. The horizontal movement mechanism includes a Y-axis encoder for detecting the position of the chuck table relative to the grinding mechanism in a direction parallel to the holding surface. The vertical movement mechanism includes a Z-axis encoder that detects the position of the grinding mechanism relative to the chuck table in a direction perpendicular to the holding surface. The control unit is An infeed grinding control unit that performs infeed grinding by rotating the chuck table to grind a workpiece, turns on the air bearing to rotate the chuck table, uses the horizontal movement mechanism to position the grinding wheel so that it passes through the center of the workpiece held on the holding surface, controls the grinding mechanism to rotate the grinding wheel, uses the vertical movement mechanism to move either the chuck table or the grinding mechanism in a direction that approaches the other relative to it, and grinds the workpiece with the grinding wheel, A grinding apparatus comprising a creep-feed grinding control unit that, when performing creep-feed grinding in which a workpiece is ground without rotating the chuck table, turns off the air bearing to prevent rotation of the chuck table, uses the vertical movement mechanism to position the lower surface of the grinding wheel below the upper surface of the workpiece on the outside of the workpiece, controls the grinding mechanism to rotate the grinding wheel, and uses the horizontal movement mechanism to move either the chuck table or the grinding mechanism horizontally relative to the other, thereby grinding the workpiece with the grinding wheel.

2. A retaining surface height measuring device for measuring the height of the retaining surface, A storage unit that stores either the height position of the grinding mechanism when the lower surface of the grinding wheel is in contact with the holding surface when the air bearing is turned ON, or the height position of the grinding mechanism when the lower surface of the grinding wheel is in contact with the holding surface when the air bearing is turned OFF, A height position calculation unit calculates the height position of the grinding mechanism that is not stored in the storage unit, using the height position of the grinding mechanism stored in the storage unit, and the difference between the height of the holding surface when the air bearing is ON and the height of the holding surface when the air bearing is OFF. The grinding apparatus according to claim 1, comprising:

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