Grinding evaluation method

Abstract

To provide a grinding evaluation method capable of simplifying evaluation of wafer grinding executed by a grinding wheel.SOLUTION: A grinding evaluation method for evaluating wafer grinding executed by a grinding wheel comprises: a holding step of holding a wafer on a chuck table; a first preparation step of adjusting a positional relationship between the chuck table and a first grinding wheel so that a point away by a prescribed distance from a rotary shat of the chuck table can overlap a rotational track of a first grindstone included in the first grinding wheel; a preparation grinding step of grinding the outer periphery of a wafer by contacting the first grindstone with the outer periphery of the wafer to grind the outer periphery of the wafer and form a projected part around the wafer; a second preparation step of adjusting a positional relationship between the chuck table and a second grinding wheel so that the rotary shat of the chuck table can overlap a rotational track of a second grindstone included in the second grinding wheel; and an evaluation grinding step of contacting the second grindstone with the projected part to grind the projected part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a grinding evaluation method for evaluating the grinding of a wafer by a grinding wheel.

Background Art

[0002] In the manufacturing process of device chips, a wafer in which devices are formed in a plurality of regions partitioned by a plurality of streets (lines to be divided) intersecting each other is used. By dividing this wafer along the streets, a plurality of device chips each having a device can be obtained. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, device chips are also required to be thinned. Therefore, before dividing the wafer, a process of grinding and thinning the wafer using a grinding device may be performed. The grinding device includes a chuck table including a holding surface for holding a workpiece, and a grinding unit for grinding the workpiece, and a grinding wheel including a grinding stone is attached to the grinding unit. The grinding device grinds the workpiece by rotating the grinding wheel and bringing the grinding stone into contact with the workpiece.

[0004] When grinding a wafer with a grinding device, it is preferable to make the holding surface of the chuck table and the surface (grinding surface) in contact with the wafer of the grinding stone parallel so that the thickness of the ground wafer becomes uniform. Therefore, before grinding the wafer, a process called self-grinding of grinding the holding surface of the chuck table with a grinding stone may be performed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to grind a wafer as intended by a grinding apparatus, it is necessary to appropriately set grinding conditions such as the feed rate of the grinding wheel, the rotational speed of the grinding wheel, and the particle size of the abrasive grains contained in the grinding wheel. Therefore, before grinding a wafer (product wafer) used in the production of an actual product, a test wafer having the same size as the product wafer is preliminarily ground experimentally with a grinding wheel, and grinding conditions suitable for grinding the product wafer are selected based on the grinding results of the test wafer.

[0007] Note that the grinding conditions suitable for grinding a product wafer vary depending on the size of the product wafer. Therefore, when product wafers of various sizes are ground by a grinding apparatus, it is necessary to select grinding conditions for each size of the product wafer. Accordingly, when selecting grinding conditions, a plurality of test wafers having different sizes are held by a chuck table and ground by a grinding wheel.

[0008] However, the chuck table mounted on the grinding apparatus is designed according to the size of the workpiece to be processed. Therefore, when grinding a plurality of test wafers having different sizes by a grinding apparatus, it is necessary to replace the chuck table each time the size of the test wafer is changed and perform self-grinding on the holding surface of the chuck table. As a result, the labor and time required for selecting grinding conditions increase.

[0009] The present invention has been made in view of such problems, and an object thereof is to provide a grinding evaluation method capable of simplifying the evaluation of wafer grinding by a grinding wheel.

Means for Solving the Problems

[0010] According to one aspect of the present invention, there is provided a grinding evaluation method for evaluating the grinding of a wafer by a grinding wheel, comprising: holding the wafer by a chuck table having a holding surface and a rotation axis set along a direction perpendicular to the holding surface; Test a holding step of holding the wafer; after the holding step, a first preparation step of adjusting the positional relationship between the chuck table and the first grinding wheel so that a point at a predetermined distance from the rotation axis of the chuck table along a direction parallel to the holding surface overlaps with the rotation orbit of a first grinding stone included in the first grinding wheel; after the first preparation step, while rotating the chuck table and the first grinding wheel, relatively moving the chuck table and the first grinding wheel along a direction perpendicular to the holding surface to bring the first grinding stone into contact with Test the outer peripheral portion of the wafer, thereby Test grinding the outer peripheral portion of the wafer to form Test a convex portion having a radius corresponding to the predetermined distance at the center portion of the wafer; corresponding to the wafer for the product a preparatory grinding step; after the preparatory grinding step, a second preparation step of adjusting the positional relationship between the chuck table and the second grinding wheel so that the rotation axis of the chuck table overlaps with the rotation orbit of a second grinding stone included in the second grinding wheel; after the second preparation step, while rotating the chuck table and the second grinding wheel, relatively moving the chuck table and the second grinding wheel along a direction perpendicular to the holding surface to bring the second grinding stone into contact with the convex portion, thereby grinding the convex portion; and evaluate the grinding of the wafer for the product based on the grinding result of the convex portion an evaluation grinding step. A grinding evaluation method including these steps is provided.

[0011] Preferably, the first grinding wheel and the second grinding wheel are the same grinding wheel, and the first grinding stone and the second grinding stone are the same grinding stone.

Advantages of the Invention

[0012] In the grinding evaluation method according to one aspect of the present invention, after grinding the outer peripheral portion of the wafer held by the chuck table with a first grinding wheel to form a convex portion at the center portion of the wafer, the convex portion is ground with a second grinding wheel. As a result, it becomes possible to evaluate the grinding of a product wafer having an arbitrary size smaller in diameter than the wafer by using a chuck table that conforms to the size of the wafer. As a result, the replacement operation of the chuck table and the self-grinding of the holding surface are omitted, and the process of grinding evaluation is simplified.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding device that can be used for implementing the grinding evaluation method according to this embodiment will be described. FIG. 1 is a partial cross-sectional side view showing the grinding device 2. In FIG. 1, the X-axis direction (the first horizontal direction, the front-rear direction) and the Y-axis direction (the second horizontal direction, the left-right direction) are perpendicular to each other. Also, the Z-axis direction (the machining feed direction, the vertical direction, the up-down direction, the height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0015] The grinding device 2 includes a base 4 that supports or houses each component constituting the grinding device 2. An opening 4a in the shape of a rectangular parallelepiped is provided on the upper surface side of the base 4. And inside the opening 4a, a chuck table (holding table) 6 for holding a workpiece to be machined by the grinding device 2 is provided. The upper surface of the chuck table 6 is a flat surface generally parallel to the X-axis direction and the Y-axis direction, and constitutes a holding surface 6a for holding the workpiece.

[0016] Also, a moving mechanism (moving unit) 8 is provided inside the base 4. The moving mechanism 8 is connected to the chuck table 6 and moves the chuck table 6 along the X-axis direction. Specifically, the moving mechanism 8 includes a ball screw 10 arranged along the X-axis direction. The ball screw 10 is screwed into a nut portion (not shown) connected to the chuck table 6. Also, a pulse motor 12 for rotating the ball screw 10 is connected to an end of the ball screw 10. When the ball screw 10 is rotated by the pulse motor 12, the chuck table 6 moves along the X-axis direction.

[0017] Also, a rotational drive source (not shown) such as a motor is connected to the chuck table 6. This rotational drive source rotates the chuck table 6 around a rotation axis (a rotation axis generally parallel to the Z-axis direction) that is generally perpendicular to the holding surface 6a. That is, the rotation axis of the chuck table 6 is set along a direction perpendicular to the holding surface 6a (see FIG. 2).

[0018] Behind the chuck table 6 and the moving mechanism 8 (on the right side of the paper surface in FIG. 1), a rectangular parallelepiped-shaped support structure (column) 14 is provided. And a moving mechanism (moving unit) 16 is provided on the surface side (front side) of the support structure 14. The moving mechanism 16 moves the chuck table 6 and a grinding unit 28 described later closer to and away from each other along a direction (Z-axis direction) perpendicular to the holding surface 6a of the chuck table 6.

[0019] Specifically, the moving mechanism 16 includes a pair of guide rails 18 fixed to the surface side of the support structure 14. The pair of guide rails 18 are arranged along the Z-axis direction while being separated from each other in the Y-axis direction. Also, a flat plate-shaped moving plate 20 is mounted on the pair of guide rails 18 in a slidable state along the guide rails 18.

[0020] A nut portion 22 is provided on the back surface side (rear side) of the moving plate 20. Also, a ball screw 24 is provided between the pair of guide rails 18 along the Z-axis direction, and the ball screw 24 is screwed into the nut portion 22. A pulse motor 26 for rotating the ball screw 24 is connected to an end of the ball screw 24. When the ball screw 24 is rotated by the pulse motor 26, the moving plate 20 moves (ascends and descends) in the Z-axis direction along the guide rails 18.

[0021] A grinding unit 28 for grinding a workpiece is mounted on the surface side (front side) of the moving plate 20. The grinding unit 28 includes a hollow cylindrical support member 30 fixed to the surface side of the moving plate 20. A cylindrical housing 32 is accommodated in the support member 30. The lower surface side of the housing 32 is supported by the bottom surface of the support member 30 via a buffer member 34 made of rubber or the like.

[0022] The housing 32 houses a cylindrical spindle 36 arranged along the Z-axis direction. The tip (lower end) of the spindle 36 is exposed from the housing 32 and protrudes downward from the lower surface of the support member 30 through an opening provided at the bottom of the support member 30. Also, a rotational drive source (not shown) such as a motor for rotating the spindle 36 is connected to the base end (upper end) of the spindle 36.

[0023] A disc-shaped mount 38 made of metal or the like is fixed to the tip of the spindle 36. An annular grinding wheel 40 for grinding the workpiece is mounted on the lower surface side of the mount 38. For example, the grinding wheel 40 is fixed to the mount 38 by a fixture such as a bolt.

[0024] The grinding wheel 40 includes an annular base 42 made of a metal such as aluminum or stainless steel and formed to have approximately the same diameter as the mount 38. The upper surface side of the base 42 is fixed to the lower surface side of the mount 38. Also, a plurality of grinding grains 44 are fixed to the lower surface side of the base 42. For example, the plurality of grinding grains 44 are formed in a rectangular parallelepiped shape and are arranged annularly at approximately equal intervals along the circumferential direction of the base 42.

[0025] The grinding grains 44 are formed by fixing abrasive grains made of diamond, cBN (cubic Boron Nitride), or the like with a binder (bonding material) such as a metal bond, a resin bond, or a vitrified bond. However, there are no restrictions on the material, shape, structure, size, etc. of the grinding grains 44. Also, the number of the grinding grains 44 can be arbitrarily set.

[0026] Each component of the grinding device 2 (the chuck table 6, the moving mechanism 8, the moving mechanism 16, the grinding unit 28, etc.) is connected to a control unit (control section, control device) 46 that controls the grinding device 2. The control unit 46 generates a control signal for controlling the operation of the components of the grinding device 2 and controls the operation of the grinding device 2.

[0027] For example, the control unit 46 is constituted by a computer and includes an arithmetic unit that performs calculations necessary for the operation of the grinding device 2, and a storage unit that stores various types of information (data, programs, etc.) used for the operation of the grinding device 2. The arithmetic unit is configured to include a processor such as a CPU (Central Processing Unit). Further, the storage unit is configured to include memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) that function as a main storage device, an auxiliary storage device, etc.

[0028] The workpiece to be machined by the grinding device 2 is held by the chuck table 6 and ground by the grinding unit 28. FIG. 2 is a perspective view showing the chuck table 6 and the grinding unit 28.

[0029] The chuck table 6 includes a columnar frame body (main body portion) 48 made of a metal such as SUS (stainless steel), glass, ceramics, resin, etc. A columnar concave portion 48b is provided at the central portion on the upper surface 48a side of the frame body 48. Further, a disk-shaped holding member 50 made of a porous member such as porous ceramics is fitted into the concave portion 48b. The holding member 50 includes a hole (flow path) communicating from the upper surface to the lower surface of the holding member 50 inside. The upper surface of the holding member 50 constitutes a circular suction surface 50a that sucks the workpiece when the chuck table 6 holds the workpiece.

[0030] Note that the depth of the concave portion 48b and the thickness of the holding member 50 are set to be approximately the same, and the upper surface 48a of the frame body 48 and the suction surface 50a of the holding member 50 are arranged on substantially the same plane. Then, the holding surface 6a of the chuck table 6 is constituted by the upper surface 48a of the frame body 48 and the suction surface 50a of the holding member 50. The holding surface 6a is connected to a suction source (not shown) such as an ejector via a hole included in the holding member 50, a flow path (not shown) formed inside the frame body 48, a valve (not shown), etc.

[0031] The workpiece is placed on the chuck table 6 so as to cover the entire suction surface 50a of the holding member 50. When the suction force (negative pressure) of the suction source is applied to the holding surface 6a in this state, the workpiece is suction-held by the chuck table 6.

[0032] A grinding wheel 40 is mounted on the grinding unit 28. The grinding wheel 40 rotates around a rotation axis (a rotation axis generally parallel to the Z-axis direction), which is generally perpendicular to the holding surface 6a of the chuck table 6, by the power transmitted through the spindle 36 and the mount 38 from a rotation drive source (not shown) connected to the base end portion of the spindle 36. That is, the rotation axis of the grinding wheel 40 is set along a direction perpendicular to the holding surface 6a.

[0033] When the grinding wheel 40 is rotated, the plurality of grinding wheels 44 move along an annular rotation orbit (travel path) generally parallel to the holding surface 6a (horizontal direction, XY plane direction). Then, by bringing the rotating grinding wheel 44 into contact with the workpiece held by the chuck table 6, the workpiece is ground.

[0034] A grinding fluid supply path (not shown) for supplying a liquid such as pure water (grinding fluid) is provided inside or in the vicinity of the grinding unit 28. When the workpiece is ground by the grinding unit 28, the grinding fluid is supplied to the workpiece and the grinding wheel 44. Thereby, the workpiece and the grinding wheel 44 are cooled, and the chips (grinding chips) generated by the grinding process are washed away.

[0035] The grinding device 2 grinds a wafer (product wafer) used in the manufacture of products such as device chips. For example, the product wafer is a disk-shaped wafer made of a semiconductor material such as silicon, and is partitioned into a plurality of rectangular regions by a plurality of streets (division planned lines) arranged in a grid pattern so as to intersect each other. Further, devices such as IC (Integrated Circuit), LSI (Large Scale Integration), LED (Light Emitting Diode), and MEMS (Micro Electro Mechanical Systems) devices are formed in each of the plurality of regions partitioned by the streets.

[0036] By dividing the product wafer along the street, a plurality of device chips each having a device are manufactured. Further, if the product wafer is ground and thinned by the grinding device 2 before dividing the product wafer, a thinned device chip can be obtained.

[0037] However, there are no restrictions on the type, material, size, shape, structure, etc. of the product wafer. For example, the product wafer may be a disk-shaped wafer made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Further, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the device, and the device may not be formed on the product wafer.

[0038] In order to grind the product wafer as intended by the grinding device 2, it is necessary to appropriately set grinding conditions such as the feed rate of the grinding wheel 40, the rotational speed of the grinding wheel 40, and the particle size of the abrasive grains contained in the grinding wheel 44. Therefore, before grinding the product wafer, a test wafer (test wafer) having the same size as the product wafer is ground experimentally with the grinding wheel 40 in advance, and an operation of selecting grinding conditions suitable for grinding the product wafer based on the grinding result of the test wafer is performed.

[0039] Note that the grinding conditions suitable for grinding the product wafer vary depending on the size of the product wafer. Therefore, when the grinding device 2 grinds product wafers of various sizes, it is necessary to select the grinding conditions for each size of the product wafer. Accordingly, when selecting the grinding conditions, a plurality of test wafers of different sizes are held by the chuck table 6 and ground by the grinding wheel 40.

[0040] However, the chuck table 6 is designed according to the size of the workpiece to be processed. For example, the diameters of the holding surface 6a and the suction surface 50a of the chuck table 6 are set according to the diameter of the workpiece. Therefore, when grinding a plurality of test wafers of different sizes by the grinding device 2, it is necessary to replace the chuck table 6 every time the size of the test wafer is changed and perform self-grinding on the holding surface 6a of the chuck table 6. As a result, the labor and time required for selecting the grinding conditions increase.

[0041] Therefore, in the present embodiment, the outer peripheral portion of the large-diameter wafer held by the chuck table 6 is ground to form a convex portion corresponding to the small-diameter wafer at the center portion of the wafer. Thereby, it becomes possible to perform the grinding evaluation of a plurality of wafers of different sizes using one type of wafer that can be held by the chuck table 6. As a result, the replacement operation of the chuck table 6 and the self-grinding of the holding surface 6a are omitted, and the process of the grinding evaluation is simplified.

[0042] Hereinafter, a specific example of the grinding evaluation method according to the present embodiment will be described. First, the wafer 11 is held by the chuck table 6 (holding step). FIG. 3(A) is a perspective view showing the grinding device 2 in the holding step, and FIG. 3(B) is a side view showing the grinding device 2 in the holding step.

[0043] Wafer 11 is a test wafer (test wafer) used for selecting the grinding conditions of the product wafer. For example, wafer 11 is a disc-shaped wafer made of semiconductor (Si, GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc., and includes surfaces (first surface) 11a and back surfaces (second surface) 11b that are generally parallel to each other.

[0044] Note that wafer 11 is preferably made of the same material as the product wafer or a material having properties similar to those of the product wafer. Also, the diameter of wafer 11 is larger than the diameter of the product wafer. For example, when the product wafer is a silicon wafer of 6 inches or less, an 8-inch silicon wafer can be used as wafer 11.

[0045] For example, wafer 11 is placed on chuck table 6 such that the surface 11a side faces holding surface 6a and the back surface 11b side is exposed upward. At this time, the center position of wafer 11 and the center position of holding surface 6a (the rotation axis of chuck table 6) overlap, the entire surface 11a side of wafer 11 is supported by holding surface 6a, and the entire suction surface 50a (see FIG. 2) is covered by wafer 11. When the suction force (negative pressure) of the suction source is applied to holding surface 6a in this state, wafer 11 is suction-held by chuck table 6.

[0046] Note that a protective sheet for protecting wafer 11 may be attached to the surface 11a side of wafer 11. For example, as the protective sheet, a tape including a film-shaped base material formed in a circular shape and an adhesive layer (paste layer) provided on the base material is used. The base material is made of a resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, etc. Also, the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive, etc. And wafer 11 is held by holding surface 6a of chuck table 6 via the protective sheet.

[0047] Next, the positional relationship between the chuck table 6 and the first grinding wheel is adjusted (first preparation step). FIG. 4(A) is a perspective view showing the grinding apparatus 2 in the first preparation step, and FIG. 4(B) is a side view showing the grinding apparatus 2 in the first preparation step. In FIGS. 4(A) and 4(B), a point P is illustrated which is separated by a predetermined distance D along a direction (XY plane direction) parallel to the holding surface 6a from the rotation axis of the chuck table 6 (the center of the holding surface 6a, the center of the wafer 11).

[0048] In the first preparation step, a processing grinding wheel (first grinding wheel) 40A is attached to the grinding unit 28. The grinding wheel 40A includes an annular base (first base) 42A and a plurality of grinding grains (first grinding grains) 44A. The materials, structures, shapes, etc. of the base 42A and the grinding grains 44A are the same as those of the base 42 and the grinding grains 44 (see FIG. 1 etc.) described above.

[0049] Each of the plurality of grinding grains 44A contains abrasive grains (first abrasive grains). For example, diamond having an average particle size of 20 μm or more and 60 μm or less is used as the first abrasive grains. And the plurality of grinding grains 44A are arranged annularly on the lower surface side of the base 42A.

[0050] The chuck table 6 holding the wafer 11 is moved along the X-axis direction by a moving mechanism 8 (see FIG. 1) and positioned below the grinding wheel 40A. Here, in the first preparation step, the positional relationship between the chuck table 6 and the grinding wheel 40A is adjusted so that the point P and the rotation orbit of the grinding grains 44A overlap. For example, the position of the chuck table 6 in the X-axis direction is adjusted so that the front end (the left end in FIG. 4(B)) of the annular locus drawn by the end portion on the outer peripheral edge side of the base 42A among the grinding grains 44A is disposed directly above the point P when the grinding wheel 40A is rotated.

[0051] Next, by bringing the grinding wheel 44A into contact with the outer peripheral portion of the wafer 11, the outer peripheral portion of the wafer 11 is ground to form a convex portion at the center portion of the wafer 11 (preliminary grinding step). FIG. 5(A) is a perspective view showing the grinding apparatus 2 in the preliminary grinding step, and FIG. 5(B) is a side view showing the grinding apparatus 2 in the preliminary grinding step.

[0052] In the preliminary grinding step, while rotating the chuck table 6 and the grinding wheel 40A, the chuck table 6 and the grinding wheel 40A are relatively moved along the direction (Z-axis direction) perpendicular to the holding surface 6a of the chuck table 6. Specifically, the grinding unit 28 is lowered by the moving mechanism 16 (see FIG. 1), and the grinding wheel 44A is moved toward the wafer 11. As a result, the rotating grinding wheel 44A comes into contact with the outer peripheral portion 11c of the wafer 11, and the outer peripheral portion 11c of the wafer 11 is ground.

[0053] For example, the rotational speed of the chuck table 6 is set to be 60 rpm or more and 300 rpm or less, and the rotational speed of the grinding wheel 40A is set to be 3000 rpm or more and 6000 rpm or less. Also, the lowering speed (machining feed speed) of the grinding wheel 40A is set to be, for example, 1 μm / s or more and 6 μm / s or less.

[0054] When the outer peripheral portion 11c of the wafer 11 is ground by the grinding wheel 44A, only the outer peripheral portion 11c of the wafer 11 is partially thinned. As a result, a columnar convex portion 11d having a radius corresponding to the distance D remains at the center portion of the wafer 11.

[0055] Note that the distance D is set to generally match the radius of the product wafer. For example, when the product wafer is a 6-inch (diameter 150 mm) silicon wafer, the distance D is set to 75 mm. Thereby, a convex portion 11d having a shape and size generally matching those of the product wafer is formed. That is, the convex portion 11d corresponding to the product wafer is formed at the center portion of the wafer 11 by the preliminary grinding step.

[0056] Next, the positional relationship between the chuck table 6 and the second grinding wheel is adjusted (second preparation step). FIG. 6(A) is a perspective view showing the grinding apparatus 2 in the second preparation step, and FIG. 6(B) is a side view showing the grinding apparatus 2 in the second preparation step.

[0057] In the second preparation step, first, the grinding unit 28 is raised by the moving mechanism 16 (see FIG. 1) to separate the grinding wheel 40A from the wafer 11. Then, the grinding wheel 40A is removed from the grinding unit 28, and a grinding wheel for evaluation (second grinding wheel) 40B is attached to the grinding unit 28. The grinding wheel 40B is a grinding wheel to be evaluated for grinding, that is, a grinding wheel assumed to be used for grinding a product wafer.

[0058] The grinding wheel 40B includes an annular base (second base) 42B and a plurality of grinding grains (second grinding grains) 44B. The materials, structures, shapes, etc. of the base 42B and the grinding grains 44B are the same as those of the base 42 and the grinding grains 44 (see FIG. 1, etc.), respectively.

[0059] Each of the plurality of grinding grains 44B contains abrasive grains (second abrasive grains). When the grinding wheel 40B is a grinding wheel for rough grinding, for example, diamond having an average particle size of 20 μm or more and 60 μm or less is used as the second abrasive grains. When the grinding wheel 40B is a grinding wheel for finish grinding, for example, diamond having an average particle size of 0.5 μm or more and 20 μm or less is used as the second abrasive grains. The plurality of grinding grains 44B are arranged annularly on the lower surface side of the base 42B.

[0060] Then, in the second preparation step, the positional relationship between the chuck table 6 and the grinding wheel 40B is adjusted so that the rotation axis of the chuck table 6 (the center of the holding surface 6a, the center of the wafer 11, and the center of the convex portion 11d) overlaps with the rotation orbit of the grinding wheel 44B. For example, the position of the chuck table 6 in the X-axis direction is adjusted so that the front end of the annular locus (the left end in FIG. 6(B)) described by the end portion on the outer peripheral edge side of the base 42B among the grinding wheels 44B is disposed directly above the center of the wafer 11 when the grinding wheel 40B is rotated.

[0061] Next, the convex portion 11d is ground by bringing the grinding wheel 44B into contact with the convex portion 11d of the wafer 11 (evaluation grinding step). FIG. 7(A) is a perspective view showing the grinding apparatus 2 in the evaluation grinding step, and FIG. 7(B) is a side view showing the grinding apparatus 2 in the evaluation grinding step.

[0062] In the evaluation grinding step, while rotating the chuck table 6 and the grinding wheel 40B, the chuck table 6 and the grinding wheel 40B are relatively moved along the direction (Z-axis direction) perpendicular to the holding surface 6a of the chuck table 6. Specifically, the grinding unit 28 is lowered by the moving mechanism 16 (see FIG. 1), and the grinding wheel 44B is moved toward the wafer 11. As a result, the rotating grinding wheel 44B comes into contact with the convex portion 11d of the wafer 11, and the convex portion 11d is ground.

[0063] For example, the rotation speed of the chuck table 6 is set to 60 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 40A is set to 3000 rpm or more and 6000 rpm or less. Further, the lowering speed (machining feed speed) of the grinding wheel 40A is appropriately set according to the type of the grinding wheel 40B. When the grinding wheel 40B is a rough grinding wheel, the machining feed speed is set to, for example, 1 μm / s or more and 6 μm / s or less. When the grinding wheel 40B is a finish grinding wheel, the machining feed speed is set to, for example, 0.5 μm / s or more and 2 μm / s or less.

[0064] The grinding of the convex portion 11d by the grinding wheel 40B proceeds in the same manner as when grinding a product wafer with a radius D using the grinding wheel 40B. That is, by grinding the convex portion 11d with the grinding wheel 40B, the grinding of the product wafer by the grinding wheel 40B can be virtually simulated. As a result, it becomes possible to evaluate the grinding of the product wafer by the grinding wheel 40B.

[0065] For example, during the grinding of the convex portion 11d by the grinding wheel 40B, values related to grinding (the load applied to the grinding wheel 40B, the current value (torque) of the motor that rotates the spindle 36, etc.) are measured. Also, after grinding the convex portion 11d, the state of the convex portion 11d (such as the surface roughness of the convex portion 11d) and the state of the grinding wheel 40B (such as the wear amount of the grinding wheel 44B) are measured. Then, based on these measurement results, the grinding conditions for grinding the product wafer with the grinding wheel 40B are selected.

[0066] Note that by adjusting the distance D in the first preparation step (see FIGS. 4(A) and 4(B)), convex portions 11d of any size can be ground in the evaluation grinding step. As a result, the evaluation of grinding when grinding a product wafer of any size with the grinding wheel 40B can be carried out using the wafer 11. For example, when using an 8-inch silicon wafer as the wafer 11, convex portions 11d corresponding to 2-inch to 6-inch silicon wafers can be ground in the evaluation grinding step.

[0067] The grinding of the wafer 11 by the above-described grinding apparatus 2 is realized by controlling the operations of the respective components of the grinding apparatus 2 with a control unit 46 (see FIG. 1). Specifically, in a storage unit (memory) of the control unit 46, a program is stored that describes a series of operations of the components of the grinding apparatus 2 necessary to sequentially perform a holding step, a first preparation step, a preparatory grinding step, a second preparation step, and an evaluation grinding step. Then, when performing grinding evaluation, the control unit 46 reads out the program from the storage unit and executes it, and sequentially outputs control signals to the components of the grinding apparatus 2. Thereby, the operation of the grinding apparatus 2 is controlled, and the grinding evaluation method according to the present embodiment is automatically performed.

[0068] As described above, in the grinding evaluation method according to the present embodiment, after grinding the outer peripheral portion 11c of the wafer 11 held by the chuck table 6 with the grinding wheel 44A to form a convex portion 11d at the center portion of the wafer 11, the convex portion 11d is ground with the grinding wheel 44B. Thereby, it becomes possible to evaluate the grinding of a product wafer having an arbitrary size smaller in diameter than the wafer 11 by using the chuck table 6 that conforms to the size of the wafer 11. As a result, the replacement operation of the chuck table 6 and the self-grinding of the holding surface 6a are omitted, and the process of grinding evaluation is simplified.

[0069] In the above embodiment, the case where the grinding wheel 40A (see FIGS. 5(A) and 5(B)) for grinding the outer peripheral portion 11c of the wafer 11 and the grinding wheel 40B (see FIGS. 7(A) and 7(B)) for grinding the convex portion 11d of the wafer 11 are different has been described. However, the grinding wheel to be the object of grinding evaluation can also be used for grinding the outer peripheral portion 11c of the wafer 11. In this case, the grinding wheel 40A and the grinding wheel 40B become the same grinding wheel, and the grinding wheel 44A and the grinding wheel 44B become the same grinding wheel. Thereby, the operation of replacing the grinding wheel 40A with the grinding wheel 40B can be omitted between the preparatory grinding step and the evaluation grinding step.

[0070] Further, the grinding device 2 may include two sets of grinding units 28. In this case, the preliminary grinding step is performed by one of the grinding units 28 with the grinding wheel 40A mounted thereon, and the evaluation grinding step is performed by the other grinding unit 28 with the grinding wheel 40B mounted thereon. Thereby, even if the grinding wheel 40A and the grinding wheel 40B are different grinding wheels, the operation of replacing the grinding wheel becomes unnecessary.

[0071] Furthermore, the wafer 11 may be processed by two grinding devices 2. In this case, the grinding wheel 40A is mounted on the grinding unit 28 of one of the grinding devices 2, and the grinding wheel 40B is mounted on the grinding unit 28 of the other grinding device 2. Then, the preliminary grinding step is performed by one of the grinding devices 2, and the evaluation grinding step is performed by the other grinding device 2.

[0072] In addition, the structure, method, etc. according to the above embodiment can be appropriately changed and implemented without departing from the scope of the object of the present invention.

Explanation of Reference Numerals

[0073] 11 Wafer 11a Front surface (first surface) 11b Back surface (second surface) 11c Outer peripheral portion 11d Protrusion 2 Grinding device 4 Base 4a Opening 6 Chuck table (holding table) 6a Holding surface 8 Moving mechanism (moving unit) 10 Ball screw 12 Pulse motor 14 Support structure (column) 16 Moving mechanism (moving unit) 18 Guide rail 20 Moving plate 22 Nut portion 24 Ball screw 26 Pulse motor 28 Grinding Unit 30 Support Member 32 Housing 34 Buffer Member 36 Spindle 38 Mount 40 Grinding Wheel 40A Grinding Wheel (First Grinding Wheel) 40B Grinding Wheel (Second Grinding Wheel) 42 Base 42A Base (First Base) 42B Base (Second Base) 44 Grinding Stone 44A Grinding Stone (First Grinding Stone) 44B Grinding Stone (Second Grinding Stone) 46 Control Unit (Control Section, Control Device) 48 Frame (Main Body Section) 48a Upper Surface 48b Recess 50 Holding Member 50a Suction Surface

Claims

1. A grinding evaluation method for evaluating the grinding of a wafer by a grinding wheel, comprising: a holding step of holding a test wafer by a chuck table including a holding surface and having a rotation axis set along a direction perpendicular to the holding surface; a first preparation step of adjusting the positional relationship between the chuck table and the first grinding wheel after the holding step so that a point at a predetermined distance from the rotation axis of the chuck table along a direction parallel to the holding surface overlaps with the rotation orbit of a first grinding stone included in the first grinding wheel; a preparatory grinding step of grinding the outer peripheral portion of the test wafer to form a convex portion corresponding to a product wafer having a radius corresponding to the predetermined distance at the center portion of the test wafer by rotating the chuck table and the first grinding wheel and relatively moving the chuck table and the first grinding wheel along a direction perpendicular to the holding surface to bring the first grinding stone into contact with the outer peripheral portion of the test wafer after the first preparation step; a second preparation step of adjusting the positional relationship between the chuck table and the second grinding wheel after the preparatory grinding step so that the rotation axis of the chuck table overlaps with the rotation orbit of a second grinding stone included in the second grinding wheel; an evaluation grinding step of grinding the convex portion by rotating the chuck table and the second grinding wheel and relatively moving the chuck table and the second grinding wheel along a direction perpendicular to the holding surface to bring the second grinding stone into contact with the convex portion and evaluating the grinding of the product wafer based on the grinding result of the convex portion after the second preparation step. The grinding evaluation method is characterized by including the above steps.

2. The first grinding wheel and the second grinding wheel are the same grinding wheel, and the first grinding stone and the second grinding stone are the same grinding stone. The grinding evaluation method according to claim 1 is characterized by this.

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