Grinding method for workpiece

Abstract

To grind workpiece with high efficiency and high quality.SOLUTION: A method for grinding workpiece for grinding workpiece using a grinding device including a chuck table, and a grinding unit for grinding workpiece held by the chuck table with a grinding wheel includes: a first grinding step of rotating the chuck table around a table rotation axis and rotationally moving the grinding wheel on a circular orbit, bringing the grinding wheel into contact with the workpiece and grinding the outer peripheral part of the workpiece; and a second grinding step of rotating the chuck table around the table rotation axis and rotationally moving the grinding wheel on the circular orbit, bringing the grinding wheel into contact with the workpiece and grinding a central part of the workpiece, after the first grinding step.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece using a grinding device that includes a chuck table having a holding surface on its upper surface and a grinding unit equipped with a grinding wheel having grinding stones arranged in an annular shape. [Background technology]

[0002] In the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, first, multiple intersecting dividing lines (streets) are set on the surface of a wafer made of a material such as a semiconductor. Then, devices such as ICs (Integrated Circuits) and LSIs (Large-scale Integration) are formed in each area defined by the dividing lines. The wafer is then divided along the dividing lines to form individual device chips.

[0003] In recent years, SiC wafers have been used to manufacture device chips equipped with power devices capable of high-temperature operation and high-voltage resistance. SiC wafers are manufactured by cutting a cylindrical SiC ingot. For example, a laser beam with a wavelength that can penetrate SiC is focused at a depth corresponding to the thickness of the wafer to be manufactured, and the SiC ingot is irradiated with the laser beam. This forms a modified layer inside the SiC ingot, which serves as the starting point for delamination (see Patent Document 1).

[0004] Damage caused by peeling and the formation of modified layers remains on the surface of SiC wafers sliced ​​from SiC ingots. Therefore, the surface of the SiC wafer is ground to remove the damaged layer, and further grinding is carried out to flatten the surface. Grinding of workpieces such as SiC wafers is performed using a grinding device. The grinding device for grinding wafers includes a chuck table capable of holding the workpiece and a grinding unit equipped with a grinding wheel having grinding stones arranged in a ring shape (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-111143 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-90389 Summary of the Invention [Problem to be solved by the invention]

[0006] Grinding a damaged layer tends to wear the grinding wheel rapidly. Therefore, in order to reduce the frequency of replacing the grinding wheel, it is desirable to use a grinding wheel that is less likely to wear. On the other hand, when grinding after removing the damaged layer, glazing and the like tend to occur, causing the condition of the grinding wheel to rapidly deteriorate. Therefore, it is desirable to use a grinding wheel that is easily worn. If a grinding wheel that is easily worn is used, the grinding wheel will wear at a rate that is sufficient to keep up with the rate of progression of glazing and the like, so unused abrasive grains will be exposed one after another, and the performance of the grinding wheel will be easily maintained.

[0007] However, when grinding a workpiece that includes parts with different grinding easiness, it is not practical to switch the type of grinding wheel during the grinding process. If an attempt is made to grind such a workpiece with a single grinding wheel, the grinding wheel will wear out excessively, necessitating frequent replacement of the grinding wheel, and the workpiece will not be ground to a satisfactory quality.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for grinding a workpiece, which can grind the workpiece with high efficiency and high quality. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a grinding unit having a holding surface, capable of suction-holding a workpiece placed on the holding surface and rotatable around a table rotation axis passing through the center of the holding surface, a spindle along the table rotation axis on which a grinding wheel having grinding stones arranged in a ring is attached at its tip, the grinding wheel being rotated by rotating the spindle, and the grinding stone being rotated and moved around a circular orbit while grinding the workpiece held on the chuck table with the grinding stone, a first moving mechanism for relatively moving the chuck table and the grinding unit in a first direction along the table rotation axis, and the chuck table and the grinding unit are connected to the first moving mechanism. a second moving mechanism that moves the chuck table and the grinding unit relatively along a second direction perpendicular to the first direction, the second moving mechanism moving the chuck table and the grinding unit relatively to each other so that the center of the holding surface and the circular orbit of the grinding wheel do not overlap along the first direction, the chuck table is rotated around the table rotation axis and the spindle is rotated to rotate the grinding wheel on the circular orbit, and the chuck table and the grinding unit are moved relatively to each other by the first moving mechanism to bring the grinding wheel into contact with the workpiece and grind the outer periphery of the workpiece. (However, this does not include cases where only a portion of the bottom surface of the grinding wheel comes into contact with the workpiece.) a first grinding step; and a second grinding step after the first grinding step, in which the chuck table and the grinding unit are moved relatively by the second moving mechanism so that the center of the holding surface and the circular orbit of the grinding wheel overlap along the first direction, the chuck table is rotated around the table rotation axis and the spindle is rotated to rotate the grinding wheel on the circular orbit, and the chuck table and the grinding unit are moved relatively by the first moving mechanism so that the grinding wheel comes into contact with the workpiece and grinds the center of the workpiece.

[0010] Preferably, the method further comprises, following the second grinding step, a third grinding step in which the outer periphery and the center of the workpiece are ground with the grinding wheel without operating the second moving mechanism.

[0011] More preferably, the workpiece to be ground by the grinding wheel has a first layer and a second layer located inside the first layer on the grinding surface side, and the grinding wheel is less likely to wear when grinding the second layer than when grinding the first layer. [Effects of the Invention]

[0012] In a method for grinding a workpiece according to one aspect of the present invention, the entire surface of the workpiece is not ground all at once, but rather the outer periphery of the workpiece is ground in a first grinding step, and then the center of the workpiece is ground in a second grinding step. As a result, the degree of change in the state of the grinding wheel in each of the first and second grinding steps is smaller than the degree of change in the state of the grinding wheel when the entire surface of the workpiece is ground all at once.

[0013] In other words, the amount of fluctuation in the state of the grinding wheel in each grinding step in the method for grinding a workpiece according to one aspect of the present invention is smaller than the amount of fluctuation in the state of the grinding wheel when the entire surface of the workpiece is ground simultaneously. In other words, the change in the state of the grinding wheel can be averaged out. This prevents excessive wear and excessive progression of glazing of the grinding wheel, allowing the grinding wheel to be used stably for a long period of time. More specifically, the grinding wheel replacement frequency can be reduced, improving the grinding efficiency of the workpiece and preventing a decrease in processing quality due to glazing of the grinding wheel.

[0014] Therefore, the present invention provides a method for grinding a workpiece that can grind the workpiece efficiently and with high quality. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view schematically showing a grinding device. [Figure 2]FIG. 2 is a cross-sectional view schematically showing a grinding device. [Figure 3] Figure 3(A) is a side view schematically showing the positional relationship between the grinding wheel and the chuck table in the first grinding step in the first example, and Figure 3(B) is a side view schematically showing the workpiece being ground in the first grinding step in the first example. [Figure 4] Figure 4(A) is a plan view schematically showing the positional relationship between the grinding wheel and the chuck table in the first grinding step in the first example, and Figure 4(B) is a plan view schematically showing the workpiece ground in the first grinding step in the first example. [Figure 5] Figure 5(A) is a side view schematically showing the positional relationship between the grinding wheel and the chuck table in the first grinding step in the second example, and Figure 5(B) is a side view schematically showing the workpiece being ground in the first grinding step in the second example. [Figure 6] Figure 6(A) is a plan view schematically showing the positional relationship between the grinding wheel and the chuck table in the first grinding step in the second example, and Figure 6(B) is a plan view schematically showing the grinding area of ​​the workpiece ground in the first grinding step in the second example. [Figure 7] Figure 7(A) is a side view schematically showing the positional relationship between the grinding wheel and the chuck table in the second grinding step, and Figure 7(B) is a side view schematically showing the workpiece being ground in the second grinding step. [Figure 8] FIG. 8(A) is a plan view schematically showing the positional relationship between the grinding wheel and the chuck table in the second grinding step, and FIG. 8(B) is a plan view schematically showing the ground workpiece. [Figure 9] Figure 9(A) is a graph showing a schematic representation of the change in the state of a grinding wheel over time when the entire surface of a workpiece is ground simultaneously, and Figure 9(B) is a graph showing a schematic representation of the change in the state of a grinding wheel over time in a method for grinding a workpiece according to an embodiment. [Figure 10] 1 is a flowchart illustrating a flow of a method for grinding a workpiece according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In a method for grinding a workpiece according to this embodiment, the workpiece is ground using a grinding device. First, the workpiece to be ground using the grinding device will be described. FIG. 3(A) includes a cross-sectional view that schematically shows the workpiece 1 before being ground, and FIG. 4(A) includes a plan view that schematically shows the workpiece 1 before being ground.

[0017] The workpiece 1 is a disk-shaped wafer made of, for example, Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductor material.

[0018] Alternatively, the workpiece 1 may be a substantially disk-shaped substrate made of a material such as sapphire, glass, or quartz. Examples of the glass include alkali glass, non-alkali glass, soda-lime glass, lead glass, borosilicate glass, and quartz glass. The workpiece 1 may also be a package substrate, a ceramic substrate, or the like. However, the workpiece 1 is not limited to these.

[0019] The surface of the workpiece 1 is divided by a plurality of planned dividing lines (not shown) arranged in a grid pattern called streets. Devices (not shown), such as ICs and LSIs, are formed in each area divided by the planned dividing lines on the surface of the workpiece 1. The workpiece 1 is ground from the back side to thin it, and then divided along the planned dividing lines to obtain individual thin device chips.

[0020] In recent years, SiC wafers have been used to manufacture device chips equipped with high-temperature, high-voltage power devices. SiC wafers are manufactured by cutting a cylindrical SiC ingot. For example, a laser beam with a wavelength that can penetrate SiC is focused at a depth corresponding to the thickness of the wafer to be manufactured, and the laser beam is irradiated onto the SiC ingot. This forms a modified layer inside the SiC ingot, which serves as the starting point for delamination.

[0021] Damage caused by peeling and the formation of modified layers remains on the surface of a SiC wafer sliced ​​from a SiC ingot. Therefore, the surface of the SiC wafer is ground to remove the damaged layer, and further grinding is performed to flatten the surface. In addition, the surface of the SiC ingot from which the SiC wafer was sliced ​​is also ground and flattened before slicing the next SiC wafer. These SiC wafers and SiC ingots can also be the workpiece 1 in the grinding method for a workpiece according to this embodiment.

[0022] Next, a grinding apparatus used in the method for grinding a workpiece according to this embodiment will be described. FIG. 1 is a perspective view schematically showing a grinding apparatus 2, and FIG. 2 is a cross-sectional view schematically showing the grinding apparatus 2. The grinding apparatus 2 has a substantially rectangular parallelepiped base 4 that supports each component. A recess 4a is formed on the top surface of the base 4 along the Y-axis direction. The recess 4a is provided with a chuck table 6 that can hold the workpiece 1 and is movable in the Y-axis direction, and a dust-proof and drip-proof cover 4b that covers the opening of the recess 4a while exposing the chuck table 6.

[0023] The dustproof and drip-proof cover 4b is omitted in Fig. 2. A Y-axis movement mechanism 8 that movably supports the chuck table 6 is disposed inside the recess 4a. The Y-axis movement mechanism 8 includes a pair of guide rails 10 extending along the Y-axis direction, a moving table 12 slidably supported on the guide rails 10, and a ball screw 16 that extends along the Y-axis direction and is threadedly engaged with a nut portion 14 provided on the underside of the moving table 12. A pulse motor 18 that rotates the ball screw 16 is connected to one end of the ball screw 16.

[0024] The chuck table 6 is disposed on the moving table 12. When the Y-axis moving mechanism 8 is operated, the chuck table 6 can be moved along the Y-axis direction. The nozzle has a ceramic frame 6a. A flow path (not shown) is provided inside the frame 6a, and one end of the flow path is connected to a suction source (not shown) such as an ejector.

[0025] The frame 6a has a recess on its upper surface, which is a disk-shaped space. A porous plate 6b, which is approximately disk-shaped, is fixed in this recess. The porous plate 6b has flat, circular lower and upper surfaces. The diameter of the porous plate 6b is approximately the same as the diameter of the workpiece 1.

[0026] The other end of the flow path of the frame 6a is connected to the lower surface of the porous plate 6b. When the suction source is operated, negative pressure is generated on the upper surface of the porous plate 6b, and the workpiece 1 is sucked and held on this upper surface. Therefore, the upper surface of the chuck table 6 functions as a holding surface 6c.

[0027] The chuck table 6 is rotatable around a table rotation axis 6e that passes through the center of the holding surface 6c and is generally perpendicular to the holding surface 6c. The tilt of the holding surface 6c of the chuck table 6 is adjustable. The grinding device 2 is equipped with a support mechanism 20 that supports the chuck table 6 rotatably and in an adjustable tilt manner.

[0028] The support mechanism 20 has an inclination adjustment mechanism having one or more fixed support members 20a and two or more movable support members 20b. For example, one fixed support member 20a and two movable support members 20b are connected to the movable table 12 at 120 degrees apart in the circumferential direction of the movable table 12. Note that only one movable support member 20b is shown in FIG. 2.

[0029] The height of the upper end of the fixed support member 20a is fixed, but the upper end of the movable support member 20b is movable in the vertical direction. By adjusting the height of the upper end of the movable support member 20b, the holding surface 6c of the chuck table 6 can be tilted at a predetermined angle with respect to the vertical direction (Z-axis direction).

[0030] A disk-shaped table base 6d is connected to the underside of the frame 6a of the chuck table 6. A drive mechanism 20c, which constitutes part of the support mechanism 20, is provided on the central underside of this table base 6d. The drive mechanism 20c includes, for example, a motor, and is connected to the frame 6a via the table base 6d. By operating the drive mechanism 20c, the chuck table 6 rotates around a table rotation axis 6e.

[0031] The grinding device 2 includes a grinding unit 22 that grinds the workpiece 1 held by the chuck table 6, and a lifting unit 24 that raises and lowers the grinding unit 22. A support part 26 is erected on the rear side of the grinding device 2, and this support part 26 supports the grinding unit 22 via the lifting unit 24. A pair of guide rails 28 that extend along the Z-axis direction (processing feed direction) are provided on the front surface of the support part 26. A moving plate 30 is slidably attached to each guide rail 28.

[0032] A nut portion 32 is provided on the back side (rear side) of the moving plate 30, and a ball screw 34 parallel to the guide rail 28 is threadedly engaged with this nut portion 32. A pulse motor 36 is connected to one end of the ball screw 34. When the ball screw 34 is rotated by the pulse motor 36, the moving plate 30 moves in the Z-axis direction along the guide rail 28.

[0033] The grinding unit 22, which grinds the workpiece, is fixed to the front side of the movable plate 30. By moving the movable plate 30, the grinding unit 22 can move in the Z-axis direction (processing feed direction). The grinding unit 22 has a cut cylindrical holding member 38. The holding member 38 is fixed to the surface on the front side of the movable plate 30.

[0034] A spindle housing 40 is provided inside the holding member 38. An annular buffer member 42 made of rubber or the like is provided at the bottom of the spindle housing 40. The spindle housing 40 is supported on the bottom surface of the holding member 38 via the buffer member 42.

[0035] A portion of the spindle 44 is rotatably housed in the spindle housing 40. A rotation drive mechanism (not shown), such as a motor, is connected to the upper end (base end) of the spindle 44. The spindle 44 is generally aligned with the table rotation axis 6e, and when the rotation drive mechanism is operated, the spindle 44 rotates around a rotation axis 46.

[0036] The lower end (tip) of the spindle 44 is located below the bottom of the holding member 38. The upper surface of a disk-shaped wheel mount 48 is connected to the lower end of the spindle 44. The upper surface of an annular grinding wheel 50 is attached to the lower surface of the wheel mount 48.

[0037] The grinding wheel 50 has an annular wheel base 52. The wheel base 52 is made of a metal such as aluminum or stainless steel, and has a diameter corresponding to the diameter of the workpiece 1. The upper surface side of this wheel base 52 is connected to the lower surface side of the wheel mount 48. In other words, the grinding wheel 50 is attached to the lower end (tip) of the spindle 44 via the wheel mount 48.

[0038] A plurality of grinding wheels 54 are provided in a circular arrangement on the underside (one surface) of the wheel base 52. Each grinding wheel 54 is formed by mixing abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as vitrified or resinoid, and then sintering the mixture. When the spindle 44 is rotated around the rotation axis 46 to rotate the grinding wheel 50, the grinding wheels 54 rotate and move on a circular orbit.

[0039] The grinding device 2 is equipped with a thickness measuring device 56 provided above the movement path of the chuck table 6. The thickness measuring device 56 measures the height from the holding surface 6c of the upper surface of the workpiece 1 held by the chuck table 6, thereby measuring the thickness of the workpiece 1. For example, the thickness measuring device 56 measures the height of the upper surface of the workpiece 1 by irradiating the upper surface of the workpiece 1 with a laser beam and detecting the reflected light, thereby measuring the thickness of the workpiece 1. However, the thickness measuring device 56 is not limited to this, and may be a contact-type thickness measuring device.

[0040] When grinding the workpiece 1 with the grinding device 2, first, the workpiece 1 is placed on the holding surface 6c, and the workpiece 1 is held by suction on the chuck table 6. At this time, the surface of the workpiece 1 to be ground is the upper surface 1a. Next, the Y-axis movement mechanism 8 is operated to move the chuck table 6 below the grinding unit 22. Thereafter, the lifting unit 24 is operated to lower the grinding unit 22, while the grinding wheel 54, which rotates and moves on a circular orbit, comes into contact with the surface to be ground, and the workpiece 1 is ground.

[0041] In the grinding process, the circular orbit of the grinding wheel 54 is positioned so that it passes above the center of the chuck table 6. Then, grinding is performed while measuring the thickness of the workpiece 1 using a thickness gauge 56 at a position away from the center of the chuck table 6.

[0042] Here, the Y-axis movement mechanism 8 may move the grinding unit 22 along the Y-axis direction, and the lifting unit 24 may lift the chuck table 6. That is, the grinding device 2 includes a first movement mechanism (lifting unit 24) that moves the chuck table 6 and the grinding unit 22 relatively along a first direction (Z-axis direction) along the table rotation axis 6e. The grinding device 2 also includes a second movement mechanism (Y-axis movement mechanism 8) that moves the two relatively along a second direction (Y-axis direction) perpendicular to the first direction.

[0043] When the workpiece 1 is ground with the grinding wheel 54, the abrasive grains contained in the grinding wheel 54 are gradually worn away, gradually reducing the grinding ability of the grinding wheel 54. On the other hand, the binder that makes up the grinding wheel 54 is also gradually worn away while the workpiece 1 is being ground, so that new abrasive grains are successively exposed on the bottom surface of the grinding wheel 54. In other words, the grinding wheel 54 is worn away from the bottom surface side while the workpiece 1 is being ground, so that the workpiece 1 can be ground with a grinding ability above a predetermined level.

[0044] Here, for example, a SiC wafer sliced ​​from a SiC ingot may be ground by a grinding device 2 as the workpiece 1. The SiC wafer has a layer on its surface that has been damaged due to peeling when the wafer is sliced ​​from the SiC ingot or the formation of a modified layer, and is ground to remove this damaged layer and flatten the surface.

[0045] FIG. 3(A) shows a schematic cross-sectional view of a workpiece 1 including a first layer 3 and a second layer 5. For example, the first layer 3 is a layer in which damage has occurred, and the second layer 5 is a layer in which no damage has occurred. However, the first layer 3 and the second layer 5 are not limited to this. Furthermore, the boundary between the first layer 3 and the second layer 5 is not necessarily clear.

[0046] Grinding the damaged layer wears the grinding wheel 54 rapidly. Therefore, it is desirable to use a grinding wheel 54 that does not wear easily in order to reduce the frequency of replacing the grinding wheel 50. On the other hand, grinding after removing the damaged layer can cause glazing and other problems, which rapidly deteriorate the condition of the grinding wheel 54, so it is desirable to use a grinding wheel 54 that wears easily. If a grinding wheel 54 that wears easily is used, the grinding wheel 54 will wear out at a rate that is sufficient to keep up with the rate at which glazing and other problems progress, so unused abrasive grains will be exposed one after another, and the performance of the grinding wheel 54 will be more likely to be maintained.

[0047] However, when grinding a workpiece 1 that includes portions with different grindability, it is not practical to change the grinding wheel 50 and switch the type of grinding stone 54 during grinding. If an attempt is made to grind such a workpiece 1 with a single grinding stone 54, the grinding stone 54 will wear out excessively, necessitating frequent replacement of the grinding stone 50, and the workpiece 1 will not be ground with sufficient quality.

[0048] Therefore, in the method for grinding a workpiece according to this embodiment, in order to prevent such problems, the workpiece 1 is ground according to the procedure described below. The method for grinding a workpiece according to this embodiment will be described in detail below. Figure 10 is a flowchart showing the flow of the method for grinding a workpiece according to this embodiment.

[0049] In the grinding method for a workpiece according to this embodiment, first, the workpiece 1 is placed on the holding surface 6c of the chuck table 6 so that the surface to be ground is exposed upward, and the workpiece 1 is held by suction on the chuck table 6. FIG. 3(A) shows a cross-sectional view of the workpiece 1 held by suction on the chuck table 6. In this case, the upper surface 1a of the workpiece 1 becomes the surface to be ground, and the lower surface 1b faces the holding surface 6c. Note that a tape-like protective member may be attached to the lower surface 1b of the workpiece 1 in advance, and the workpiece 1 may be held on the chuck table 6 via the protective member.

[0050] When the workpiece 1 is placed on the chuck table 6, the workpiece 1 is precisely positioned so that the center 7 of the workpiece 1 coincides with the center of the holding surface 6c. At this time, the planar position of the center 7 of the workpiece 1 coincides with the planar position of the center of the holding surface 6c, and the table rotation axis 6e passes through the center 7 of the workpiece 1.

[0051] Then, a first grinding step is performed to grind the outer peripheral portion 9 (described later) of the workpiece 1. First, the chuck table 6 and the grinding unit 22 are moved relatively by the second movement mechanism (Y-axis movement mechanism 8) so that the center of the holding surface 6c and the circular orbit of the grinding wheel 54 do not overlap along the first direction (Z-axis direction). FIG. 4(A) is a plan view schematically showing the positional relationship between the circular orbit 54a of the grinding wheel 54 and the chuck table 6 in this state. That is, the center of the holding surface 6c is shifted from the circular orbit 54a (S11).

[0052] Next, the chuck table 6 is rotated around the table rotation axis 6e, and the spindle 44 is rotated to rotate the grinding wheel 54 on the circular orbit 54a. Then, the chuck table 6 and the grinding unit 22 are moved in the first direction (Z-axis direction) by the first movement mechanism (lifting unit 24) so ​​as to approach each other. Then, the grinding wheel 54 comes into contact with the upper surface 1a, which is the surface to be ground, of the workpiece 1, and grinding of the workpiece 1 begins (S12).

[0053] Here, the circular orbit 54a of the grinding wheel 54 does not overlap with the center of the chuck table 6, so the area including the center 7 of the workpiece 1 is not ground. The area including the center 7 of the workpiece 1 is called the central portion 11, and the annular area surrounding the central portion 11 from the outside is called the outer periphery 9.

[0054] In this case, the grinding wheel 54 comes into contact with the workpiece 1 to grind the outer periphery 9 of the workpiece 1. This stage in which the outer periphery 9 of the workpiece 1 is ground is referred to as the first grinding step. In the first grinding step, as shown in Fig. 4(A), the innermost periphery of the outer periphery 9 to be ground comes into contact with the outermost periphery of the path of the grinding wheel 54 that rotates and moves on the circular orbit 54a.

[0055] Fig. 3(B) is a side view that schematically shows the first grinding step, and includes a cross-sectional view that schematically shows the workpiece 1 after the outer periphery 9 has been ground. Fig. 4(B) is a plan view that schematically shows the workpiece 1 after the outer periphery 9 has been ground. In the first grinding step, grinding proceeds while the thickness of the outer periphery 9 of the workpiece 1 is monitored by the thickness measuring device 56, and when it is confirmed that the outer periphery 9 has reached a predetermined thickness, the operation of the first moving mechanism (lifting unit 24) stops, and grinding of the outer periphery 9 is completed.

[0056] 4(A), the first grinding step of grinding the outer peripheral portion 9 of the workpiece 1 is not limited to the case where the innermost periphery of the outer peripheral portion 9 to be ground comes into contact with the outermost periphery of the path of the grinding wheel 54 that rotates and moves on the circular orbit 54a. Next, a first grinding step according to a second example, which is a modified example of the first grinding step according to the first example described above, will be described.

[0057] Fig. 5(A) is a side view schematically showing the workpiece 1, grinding unit 22, and chuck table 6 at the start of the first grinding step according to the second example, and Fig. 6(A) is a plan view schematically showing the first grinding step according to the second example. In the first grinding step according to the second example, as shown in Fig. 6(A), the innermost periphery of the outer peripheral portion 9 to be ground comes into contact with the innermost periphery of the path of the grinding wheel 54 that rotates and moves on a circular orbit 54a.

[0058] Fig. 5(B) is a side view that schematically shows the first grinding step according to the second example, and Fig. 6(B) is a plan view that schematically shows the workpiece 1 whose outer periphery 9 has been ground in the first grinding step according to the second example. In this case as well, when the chuck table 6 is rotated around the table rotation axis 6e and the grinding wheel 54 is rotated and moved on the circular orbit 54a, and the grinding wheel 54 is brought into contact with the upper surface 1a of the workpiece 1, the outer periphery 9 of the workpiece 1 is ground.

[0059] Whether the first grinding step according to the first example or the first grinding step according to the second example is performed, the outer periphery 9 of the workpiece 1 is ground. In addition, in Figures 4(B) and 6(B), grinding marks formed as minute irregularities on the upper surface 1a of the outer periphery 9 of the workpiece 1 are shown by dashed lines.

[0060] In the grinding method for a workpiece according to this embodiment, a second grinding step is performed after a first grinding step to grind the center portion 11 of the workpiece 1. Fig. 7(A) is a side view schematically showing the grinding unit 22, the chuck table 6, etc. at the start of the second grinding step. Fig. 8(A) is a plan view schematically showing the positional relationship between the circular orbit 54a of the grinding wheel 54 and the chuck table 6 in the second grinding step.

[0061] In the second grinding step, first, the second moving mechanism (Y-axis moving mechanism 8) is operated to relatively move the chuck table 6 and the grinding unit 22, so that the center of the holding surface 6c and the circular orbit 54a of the grinding wheel 54 are aligned along the first direction (Z-axis direction). That is, the center of the holding surface 6c is aligned with the circular orbit (S21). FIG. 8(A) is a plan view schematically showing the positional relationship between the circular orbit 54a of the grinding wheel 54 and the chuck table 6 in this state. At this time, the center 7 of the workpiece 1 is aligned with the circular orbit 54a.

[0062] Next, the chuck table 6 is rotated around the table rotation axis 6e, and the spindle 44 is rotated to rotate the grinding wheel 54 on the circular orbit 54a. Then, the chuck table 6 and the grinding unit 22 are moved in the first direction (Z-axis direction) by the first movement mechanism (lifting unit 24) so ​​as to approach each other. Then, the grinding wheel 54 comes into contact with the upper surface 1a, which is the surface to be ground, of the workpiece 1, and grinding of the workpiece 1 begins (S22).

[0063] Then, in the second grinding step, the central portion 11 of the workpiece 1 that was not ground in the first grinding step is mainly ground. Fig. 7(B) is a side view that schematically shows the second grinding step, and includes a cross-sectional view that schematically shows the workpiece 1 with the central portion 11 ground. Fig. 8(B) is a plan view that schematically shows the workpiece 1 with the central portion 11 ground.

[0064] In the second grinding step, grinding proceeds while the thickness of the central portion 11 of the workpiece 1 is monitored by the thickness measuring device 56, and when it is confirmed that the central portion 11 has reached a predetermined thickness, the operation of the first moving mechanism (lifting unit 24) stops, completing the grinding of the central portion 11. When the first grinding step and the second grinding step are performed, the entire upper surface 1a, which is the surface to be ground, of the workpiece 1 is ground, and the entire area of ​​the workpiece 1 reaches a predetermined thickness.

[0065] Here, the change in the state of the grinding wheel 54 will be described using an example in which the workpiece 1 is a SiC wafer sliced ​​from a SiC ingot. In this example, the first layer 3 exposed on the upper surface 1a of the workpiece 1 before grinding is a damaged layer, and the second layer 5 located inside (below) the first layer 3 is an undamaged layer. Then, the first layer 3 is removed by grinding, and part of the second layer 5 is also removed.

[0066] In a conventional grinding method that does not use the grinding method for a workpiece according to this embodiment, the surface to be ground of the workpiece 1 is simultaneously ground, removing the first layer 3 and grinding away a portion of the second layer 5. FIG. 9(A) is a graph that schematically illustrates the change in the state of the grinding wheel 54 during this process. In this graph, the vertical axis represents the condition (C) of the grinding wheel 54, which particularly represents the quality of the grinding ability. This condition (C) is not a numerical value based on a measurement, but a virtual index used solely to explain the change in the state of the grinding wheel 54.

[0067] When grinding of the workpiece 1 begins, the grinding wheel 54 first grinds the first layer 3, which is the layer in the SiC wafer where damage occurred. When the damaged layer is the first layer 3, the grinding wheel 54 is severely worn when grinding the first layer 3. However, as the grinding wheel 54 is worn, unused abrasive grains are successively exposed, and the condition (C) of the grinding wheel 54 rises to a predetermined level C1. However, once the condition (C) of the grinding wheel 54 exceeds the predetermined level C1, it does not improve, and the grinding wheel 54 simply continues to wear severely thereafter.

[0068] After that, the removal of the first layer 3 is completed, and the process shifts to grinding the second layer 5, which is an undamaged layer. The time required for this is called time T A In grinding the second layer 5, the grinding progresses while the condition (C) of the grinding wheel 54 deteriorates due to glazing and the like. Then, the time T B Alternatively, it may be possible that the condition (C) of the grinding wheel 54 does not meet the required standard and is in an unsuitable state for grinding the workpiece 1.

[0069] The boundary between the first layer 3 and the second layer 5 in the workpiece 1 is not always clear, and the change in the condition (C) of the grinding wheel 54 is not always linear. The change in the condition of the grinding wheel 54 does not always proceed as shown in the graph in Figure 9(A). However, the problems that arise when using a single grinding wheel 54 to grind two layers that differ in their susceptibility to wear and glazing are clearly shown in the graph in Figure 9(A).

[0070] In contrast to this, in the method for grinding a workpiece according to this embodiment, first, the outer periphery 9 of the workpiece 1 is ground to remove the first layer 3 and a portion of the second layer 5, and then the center portion 11 is ground to grind the first layer 3 and a portion of the second layer 5. In other words, because the outer periphery 9 and the center portion 11 of the workpiece 1 are ground separately, the area ground at one time is relatively small compared to when the entire top surface 1a of the workpiece 1 is ground.

[0071] FIG. 9(B) is a graph showing a schematic diagram of the change in the state of the grinding wheel 54 at this time. This graph shows the change in the state (C) of the grinding wheel 54, similar to the graph shown in FIG. 9(A). Here, at time T 1A is the time at which removal of the first layer 3 from the outer periphery 9 of the workpiece 1 is completed in the first grinding step, and time T 1B is the time when the first grinding step ends. 2A is the time at which the removal of the first layer 3 from the central portion 11 of the workpiece 1 is completed in the second grinding step, and time T 2B is the time when the second grinding step ends.

[0072] The amount of change in the condition (C) of the grinding wheel 54 is roughly proportional to the amount of the workpiece 1 ground by the grinding wheel 54. Therefore, the change in the condition (C) of the grinding wheel 54 when grinding and removing the first layer 3 of the workpiece 1 in each of the first grinding step and the second grinding step is smaller than when the entire upper surface (grinding surface) 1a of the workpiece 1 is ground simultaneously.

[0073] Similarly, the change in the state (C) of the grinding wheel 54 when grinding and removing a portion of the second layer 5 of the workpiece 1 in each of the first grinding step and the second grinding step is smaller than when the entire upper surface (grinding surface) 1a of the workpiece 1 is ground simultaneously.

[0074] For example, in the first grinding step, grinding of the first layer 3 is completed before the grinding wheel 54 is excessively worn, and grinding of the second layer 5 is completed before the condition of the grinding wheel 54 deteriorates excessively. Similarly, in the second grinding step, grinding of the first layer 3 is completed before the grinding wheel 54 is excessively worn, and grinding of the second layer 5 is completed before the condition of the grinding wheel 54 deteriorates excessively. In this way, changes in the condition (C) of the grinding wheel 54 while grinding the workpiece 1 are averaged, making it less likely that the grinding wheel 54 will wear out excessively or its condition will deteriorate excessively.

[0075] Here, the sizes of the outer periphery 9 and the central portion 11 set in the workpiece 1 will be explained using the plan view shown in Fig. 4(A). As shown in Fig. 4(A), the radius of the top surface (surface to be ground) 1a of the workpiece 1 is R, the radius of the central portion 11 is R1, and the width of the outer periphery 9 is R2. In order to smooth out changes in the state of the grinding wheel 54 as evenly as possible, it is most preferable that the areas of the outer periphery 9 and the central portion 11 are approximately equal.

[0076] To make the areas of the outer periphery 9 and the center 11 equal, the radius R1 of the center 11 should be the radius R of the upper surface (surface to be ground) 1a multiplied by 1 / √2. In this case, the width R2 of the outer periphery 9 should be the radius R of the upper surface (surface to be ground) 1a multiplied by 1-1 / √2. For example, if the workpiece 1 is a wafer with a diameter of 200 mm, the diameter of the center 11 should be approximately 141 mm, and the width of the outer periphery 9 should be approximately 30 mm.

[0077] However, the areas of the outer periphery 9 and the central portion 11 do not need to be strictly equal. The area of ​​the central portion 11 is preferably 80% to 120%, more preferably 90% to 110%, and even more preferably 95% to 105% of the area of ​​the outer periphery 9. However, the areas and ratios of the outer periphery 9 and the central portion 11 are not limited to these.

[0078] As described above, when the first grinding step and the second grinding step are performed, the outer peripheral portion 9 and the central portion 11 of the workpiece 1 are ground, respectively, and the first layer 3 and a part of the second layer 5 are removed. Here, it is not easy to precisely match the height positions of the lower ends of the grinding wheels 54 when the first grinding step and the second grinding step are completed.

[0079] For example, the height position of the lower end of grinding wheel 54 may be slightly higher when the second grinding step is completed. In this case, central portion 11 on upper surface 1a of workpiece 1 after grinding will be higher than outer periphery 9, forming a step on upper surface 1a and making it non-flat. Therefore, after grinding central portion 11 of workpiece 1 in the second grinding step, a third grinding step may be performed in which lifting unit 24 is further operated to lower grinding unit 22 and grind outer periphery 9 and central portion 11 of workpiece 1 with grinding wheel 54.

[0080] Following the second grinding step, the third grinding step is performed without operating the second moving mechanism (Y-axis moving mechanism 8), and the outer periphery 9 and the center 11 of the workpiece 1 are simultaneously ground, so that the top surfaces of the outer periphery 9 and the center 11 of the workpiece 1 are at the same height. In other words, the top surface 1a of the workpiece 1 is flattened.

[0081] Here, when the third grinding step is carried out following the second grinding step, it is preferable that the operation of the first moving mechanism (lifting unit 24) that was proceeding in the second grinding step be continued without stopping. In this case, the moment when the second grinding step ends and the moment when the third grinding step starts are not necessarily clear, and the second grinding step and the third grinding step switch seamlessly.

[0082] However, in the grinding method for a workpiece according to this embodiment, the third grinding step does not have to be performed, and a step may ultimately remain between the outer periphery 9 and the center 11 of the workpiece 1. In this case, after the grinding method for a workpiece according to this embodiment is performed, the step may be removed by performing finish grinding on the upper surface 1a of the workpiece 1 carried out from the grinding device 2 using another grinding device or by polishing using a polishing device.

[0083] As explained above, in the method for grinding a workpiece according to this embodiment, the entire surface of the workpiece 1 is not ground all at once, but rather the outer periphery 9 of the workpiece 1 is ground in the first grinding step, and then the center 11 of the workpiece 1 is ground in the second grinding step. Therefore, the degree of change in the state of the grinding wheel 54 in each of the first grinding step and the second grinding step is smaller than the degree of change in the state of the grinding wheel 54 when the entire surface of the workpiece 1 is ground all at once.

[0084] In other words, the amount of fluctuation in the state of the grinding wheel 54 in each grinding step is smaller than the amount of fluctuation in the state of the grinding wheel 54 when the entire surface of the workpiece 1 is ground simultaneously. In other words, the changes in the state of the grinding wheel 54 can be averaged out. As a result, excessive wear and excessive progression of glazing of the grinding wheel 54 can be prevented, allowing the grinding wheel 54 to be used stably for a long period of time. More specifically, the frequency of replacement of the grinding wheel 54 can be reduced, improving the grinding efficiency of the workpiece 1, and preventing a decrease in processing quality due to glazing of the grinding wheel 54, etc.

[0085] The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above-described embodiment, the upper surface (surface to be ground) 1a of the workpiece 1 is divided into the central portion 11 and the outer periphery 9, and the workpiece 1 is ground in two stages. However, the grinding method of the workpiece according to one aspect of the present invention is not limited to this. In other words, the upper surface (surface to be ground) 1a of the workpiece 1 may be divided into three or more regions, and the workpiece 1 may be ground in three or more stages.

[0086] In this case, in order to minimize changes in the state of the grinding wheel 54, it is preferable that the areas of the divided regions of the upper surface (surface to be ground) 1a of the workpiece 1 are approximately equal. The boundaries of the regions are preferably set concentrically around the center 7 of the workpiece 1. Furthermore, it is preferable that the regions are ground one after the other in order from the outside of the workpiece 1.

[0087] In the above embodiment, the grinding wheel 54 is worn out and its condition improves when the first layer 3 on the upper surface 1a of the workpiece 1 is ground, and the grinding wheel 54 is dulled and its condition deteriorates when the second layer 5 is ground. However, the workpiece 1 and the grinding wheel 54 are not limited to this. For example, the condition of the grinding wheel 54 may deteriorate when the first layer 3 is ground, and the condition of the grinding wheel 54 may improve when the second layer 5 is ground.

[0088] Furthermore, the workpiece 1 may include layers other than the first layer 3 and the second layer 5, and these layers may be ground with the grinding wheel 54. Furthermore, the boundaries between the layers included in the workpiece 1 are not necessarily clear, and the boundary between the first layer 3 and the second layer 5 is not necessarily clear. What is important in one aspect of the present invention is that the workpiece 1 is divided into multiple regions and ground sequentially, thereby reducing the range of variation in the state of the grinding wheel 54. Therefore, the workpiece 1 does not necessarily have to include the first layer 3 and the second layer 5.

[0089] The structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0090] 1 Workpiece 1a Top surface 1b Bottom side 3. First Layer 5 Second Layer 7 center 9 Outer periphery 11 Center 2 Grinding equipment 4 Foundation 4a Recess 4b Dustproof / waterproof cover 6 Chuck table 6a Frame 6b Porous plate 6c Holding surface 6d Table base 6e Table rotation axis 8 Y-axis movement mechanism (second movement mechanism) 10 Guide rail 12 Mobile Table 14 Nut part 16 Ball screw 18 Pulse motor 20 Support mechanism 20a Fixed support member 20b Movable support member 20c Drive mechanism 22 Grinding unit 24 Lifting unit 26 Support part 28 Guide rail 30 Moving Plate 32 Nut part 34 Ball screw 36 Pulse motor 38 Retaining member 40 Spindle housing 42 Cushioning material 44 Spindle 46 Rotation axis 48 Wheel Mount 50 grinding wheels 52 Wheel base 54 Grinding Wheel 54a Circular orbit 56 Thickness measuring instrument

Claims

1. a chuck table having a holding surface, capable of suction-holding a workpiece placed on the holding surface, and rotatable around a table rotation axis passing through the center of the holding surface; a grinding unit having a spindle along the table rotation axis and a grinding wheel having grinding stones arranged in a circular pattern attached to the tip thereof, the grinding wheel being rotated by rotating the spindle, and the grinding stone being rotated and moved along a circular orbit while grinding the workpiece held on the chuck table with the grinding stone; a first moving mechanism that moves the chuck table and the grinding unit relatively in a first direction along the table rotation axis; a second moving mechanism that relatively moves the chuck table and the grinding unit along a second direction perpendicular to the first direction, a first grinding step in which the chuck table and the grinding unit are moved relatively by the second moving mechanism so that the center of the holding surface and the circular orbit of the grinding wheel do not overlap along the first direction, the chuck table is rotated around the table rotation axis and the spindle is rotated to rotate the grinding wheel on the circular orbit, and the chuck table and the grinding unit are moved relatively by the first moving mechanism to bring the grinding wheel into contact with the workpiece and grind the outer periphery of the workpiece (excluding the case where only a portion of the bottom surface of the grinding wheel comes into contact with the workpiece); a second grinding step of, after the first grinding step, relatively moving the chuck table and the grinding unit by the second moving mechanism so that the center of the holding surface and the circular orbit of the grinding wheel overlap along the first direction, rotating the chuck table around the table rotation axis and rotating the spindle to rotationally move the grinding wheel on the circular orbit, and moving the chuck table and the grinding unit relatively by the first moving mechanism so that the grinding wheel comes into contact with the workpiece and grinds the center of the workpiece.

2. 2. The method for grinding a workpiece according to claim 1, further comprising a third grinding step following the second grinding step, in which the outer periphery and the center of the workpiece are ground with the grinding wheel without operating the second moving mechanism.

3. a first layer and a second layer located inside the first layer are provided on a grinding surface side of the workpiece to be ground by the grinding wheel; 3. The method for grinding a workpiece according to claim 1, wherein the grinding wheel is less likely to wear when grinding the second layer than when grinding the first layer.

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