JP2022181245A - Grinding evaluation method - Google Patents

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

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

In the process of manufacturing device chips, a wafer is used in which devices are formed in a plurality of areas partitioned by a plurality of streets (division lines) that intersect with each other. A plurality of device chips each having a device is obtained by dividing the wafer along the streets. Device chips are incorporated into various electronic devices such as mobile phones and personal computers.

In recent years, along with the miniaturization of electronic devices, there is a demand for thinner device chips. Therefore, before the wafer is divided, a process of grinding and thinning the wafer using a grinding apparatus is sometimes performed. The grinding apparatus includes a chuck table including a holding surface for holding a workpiece, and a grinding unit for grinding the workpiece, and the grinding unit is equipped with a grinding wheel including a grinding wheel. A grinding device grinds a workpiece by rotating a grinding wheel and bringing a grinding wheel into contact with the workpiece.

When grinding a wafer with a grinding machine, the holding surface of the chuck table and the surface of the grinding wheel that comes into contact with the wafer (grinding surface) are made parallel so that the thickness of the wafer after grinding is uniform. is preferred. Therefore, before grinding the wafer, a process called self-grinding is sometimes performed in which the holding surface of the chuck table is ground with a grinding wheel (see Patent Document 1).

JP 2018-94671 A

In order to grind the wafer as intended by the grinding machine, it is necessary to appropriately set the grinding conditions such as the feed rate of the grinding wheel, the rotation speed of the grinding wheel, and the grain size of the abrasive grains contained in the grinding wheel. Therefore, before grinding the wafers (product wafers) used to manufacture the actual products, test wafers (test wafers) having the same size as the product wafers are ground with a grinding wheel on a trial basis in advance. Then, the grinding conditions suitable for grinding the product wafers are selected based on the grinding results of the test wafers.

Grinding conditions suitable for grinding the 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 product wafer size. Therefore, when selecting grinding conditions, a plurality of test wafers of different sizes are held by the chuck table and ground by the grinding wheel.

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 of different sizes with a grinding device, 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.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a grinding evaluation method capable of simplifying the evaluation of wafer grinding by a grinding wheel.

According to one aspect of the present invention, there is provided a grinding evaluation method for evaluating grinding of a wafer by a grinding wheel. a holding step of holding, after the holding step, a point separated by a predetermined distance from the rotation axis of the chuck table along a direction parallel to the holding surface and a rotational trajectory of the first grinding wheel included in the first grinding wheel. a first preparation step of adjusting the positional relationship between the chuck table and the first grinding wheel such that the chuck table and the first grinding wheel overlap each other; after the first preparation step, while rotating the chuck table and the first grinding wheel, and moving the chuck table and the first grinding wheel relative to each other in a direction perpendicular to the holding surface to bring the first grinding wheel into contact with the outer periphery of the wafer, thereby removing the outer periphery of the wafer. to form a protrusion having a radius corresponding to the predetermined distance at the center of the wafer; a second preparatory step of adjusting the positional relationship between the chuck table and the second grinding wheel so that the rotational orbit of the second grinding wheel overlaps; after the second preparatory step, the chuck table and the second While rotating the second grinding wheel, the chuck table and the second grinding wheel are moved relative to each other along the direction perpendicular to the holding surface to bring the second grinding wheel into contact with the projection. and an evaluation grinding step of grinding the protrusion.

Preferably, the first grinding wheel and the second grinding wheel are the same grinding wheel, and the first grinding wheel and the second grinding wheel are the same grinding wheel.

In the grinding evaluation method according to one aspect of the present invention, the outer peripheral portion of the wafer held by the chuck table is ground by the first grinding wheel to form a convex portion in the central portion of the wafer, and then the convex portion is ground by the second grinding wheel. Grind with This makes it possible to evaluate the grinding of a product wafer of any size smaller in diameter than the wafer using a chuck table that matches the size of the wafer. As a result, the replacement work of the chuck table and the self-grinding of the holding surface are omitted, and the grinding evaluation process is simplified.

It is a partial cross-sectional side view which shows a grinding apparatus. It is a perspective view showing a chuck table and a grinding unit. FIG. 3A is a perspective view showing the grinding device in the holding step, and FIG. 3B is a side view showing the grinding device in the holding step. FIG. 4A is a perspective view showing the grinding device in the first preparation step, and FIG. 4B is a side view showing the grinding device in the first preparation step. FIG. 5A is a perspective view showing the grinding device in the preliminary grinding step, and FIG. 5B is a side view showing the grinding device in the preliminary grinding step. FIG. 6A is a perspective view showing the grinding device in the second preparation step, and FIG. 6B is a side view showing the grinding device in the second preparation step. FIG. 7A is a perspective view showing the grinding device in the evaluation grinding step, and FIG. 7B is a side view showing the grinding device in the evaluation grinding step.

An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, a configuration example of a grinding apparatus that can be used to implement the grinding evaluation method according to the present embodiment will be described. FIG. 1 is a partial cross-sectional side view showing the grinding device 2. FIG. In FIG. 1, the X-axis direction (first horizontal direction, front-rear direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. Also, the Z-axis direction (processing feed direction, vertical direction, vertical direction, height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.

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

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 . A pulse motor 12 for rotating the ball screw 10 is connected to the 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.

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

A rectangular parallelepiped support structure (column) 14 is provided behind the chuck table 6 and the moving mechanism 8 (on the right side of the paper surface of FIG. 1). 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, which will be described later, toward and away from each other along a direction perpendicular to the holding surface 6a of the chuck table 6 (the Z-axis direction).

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. A flat plate-like moving plate 20 is attached to the pair of guide rails 18 so as to be slidable along the guide rails 18 .

A nut portion 22 is provided on the back side (rear side) of the moving plate 20 . A ball screw 24 is provided along the Z-axis direction between the pair of guide rails 18 , 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 the end of the ball screw 24 . When the ball screw 24 is rotated by the pulse motor 26, the moving plate 20 moves (lifts) along the guide rail 18 in the Z-axis direction.

A grinding unit 28 for grinding a workpiece is attached to the surface side (front side) of the moving plate 20 . The grinding unit 28 includes a hollow columnar 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 cushioning member 34 made of rubber or the like.

The housing 32 accommodates a cylindrical spindle 36 arranged along the Z-axis direction. A 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 in the bottom of the support member 30 . A base end (upper end) of the spindle 36 is connected to a rotation drive source (not shown) such as a motor for rotating the spindle 36 .

A disk-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 attached to the lower surface of the mount 38 . For example, grinding wheel 40 is secured to mount 38 by fasteners such as bolts.

The grinding wheel 40 includes an annular base 42 made of metal such as aluminum or stainless steel and having 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 . A plurality of grinding wheels 44 are fixed to the lower surface of the base 42 . For example, the plurality of grinding wheels 44 are formed in a rectangular parallelepiped shape and are arranged in a ring at approximately equal intervals along the circumferential direction of the base 42 .

The grinding wheel 44 is formed by fixing abrasive grains made of diamond, cBN (cubic boron nitride) or the like with a bonding material such as a metal bond, a resin bond, or a vitrified bond. However, the material, shape, structure, size, etc. of the grinding wheel 44 are not limited. Also, the number of grinding wheels 44 can be set arbitrarily.

Each component of the grinding device 2 (chuck table 6 , moving mechanism 8 , moving mechanism 16 , 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 controls the operation of the grinding machine 2 by generating control signals that control the operation of the components of the grinding machine 2 .

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

A workpiece to be processed by the grinding device 2 is held by the chuck table 6 and ground by the grinding unit 28 . 2 is a perspective view showing the chuck table 6 and the grinding unit 28. FIG.

The chuck table 6 includes a cylindrical frame (main body) 48 made of metal such as SUS (stainless steel), glass, ceramics, resin, or the like. A cylindrical recess 48b is provided in the center of the frame 48 on the upper surface 48a side. A disk-shaped holding member 50 made of a porous material such as porous ceramics is fitted in the concave portion 48b. The holding member 50 includes therein holes (flow paths) that communicate from the upper surface to the lower surface of the holding member 50 . The upper surface of the holding member 50 forms a circular suction surface 50a for sucking the workpiece when the chuck table 6 holds the workpiece.

The depth of the recess 48b and the thickness of the holding member 50 are set to be approximately the same, and the upper surface 48a of the frame 48 and the suction surface 50a of the holding member 50 are arranged approximately on the same plane. A holding surface 6 a of the chuck table 6 is formed by the upper surface 48 a of the frame 48 and the suction surface 50 a 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 48, a valve (not shown), and the like. It is connected.

A workpiece is placed on the chuck table 6 so as to cover the entire suction surface 50 a 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 chuck table 6 sucks and holds the workpiece.

A grinding wheel 40 is attached to the grinding unit 28 . The grinding wheel 40 is driven by power transmitted from a rotary drive source (not shown) connected to the base end of the spindle 36 via the spindle 36 and the mount 38 to rotate the grinding wheel 40 on a rotary shaft substantially perpendicular to the holding surface 6 a of the chuck table 6 . (rotational axis generally parallel to the Z-axis direction). That is, the rotation axis of the grinding wheel 40 is set along the direction perpendicular to the holding surface 6a.

When the grinding wheel 40 is rotated, each of the plurality of grinding wheels 44 moves along an annular rotational orbit (movement path) substantially parallel to the holding surface 6a (horizontal direction, XY plane direction). By bringing the rotating grinding wheel 44 into contact with the workpiece held by the chuck table 6, the workpiece is ground.

A grinding liquid supply path (not shown) for supplying a liquid (grinding liquid) such as pure water is provided inside or near the grinding unit 28 . When grinding the workpiece by the grinding unit 28 , the grinding fluid is supplied to the workpiece and the grinding wheel 44 . As a result, the workpiece and the grinding wheel 44 are cooled, and debris (grinding dust) generated by the grinding process is washed away.

The grinding apparatus 2 grinds wafers (product wafers) used for manufacturing products such as device chips. For example, a 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 (planned division lines) arranged in a lattice so as to intersect each other. there is Devices such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed in each of the plurality of areas partitioned by the streets. .

A plurality of device chips each having a device are manufactured by dividing the product wafer along the streets. Further, if the product wafer is ground and thinned by the grinding device 2 before the product wafer is divided, a thinned device chip can be obtained.

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, or the like. Moreover, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the devices, and devices may not be formed on the product wafer.

In order to grind the product wafer as intended by the grinding device 2, the grinding conditions such as the feed rate of the grinding wheel 40, the number of revolutions of the grinding wheel 40, and the grain size of the abrasive grains contained in the grinding wheel 44 are appropriately set. Must be set. Therefore, before grinding the product wafer, a test wafer (test wafer) having the same size as the product wafer is ground by the grinding wheel 40 on a trial basis in advance, and the product is ground based on the grinding result of the test wafer. An operation is performed to select grinding conditions suitable for grinding the wafer for manufacturing.

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

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, the chuck table 6 is replaced each time the size of the test wafer is changed, and the holding surface 6a of the chuck table 6 is self-grinded. need to apply. As a result, the labor and time required for selecting grinding conditions increase.

Therefore, in this 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 central portion of the wafer. This makes it possible to perform 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 work of the chuck table 6 and the self-grinding of the holding surface 6a are omitted, and the grinding evaluation process is simplified.

A specific example of the grinding evaluation method according to the present embodiment will be described below. First, the chuck table 6 holds the wafer 11 (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.

The wafer 11 is a test wafer (test wafer) used for selecting grinding conditions for product wafers. For example, the wafer 11 is a disk-shaped wafer made of semiconductor (Si, GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc., and has a front surface (first surface) 11a and a rear surface ( second surface) 11b.

It is preferable that the wafer 11 is 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 the wafer 11 is larger than the diameter of the product wafer. For example, if the product wafer is a silicon wafer of 6 inches or less, an 8-inch silicon wafer can be used as the wafer 11 .

For example, the wafer 11 is placed on the chuck table 6 so that the front surface 11a side faces the holding surface 6a and the back surface 11b side is exposed upward. At this time, the center position of the wafer 11 and the center position of the holding surface 6a (rotational axis of the chuck table 6) of the wafer 11 are overlapped, the entire surface 11a side of the wafer 11 is supported by the holding surface 6a, and the suction surface 50a (see FIG. 2) is arranged so that the entirety of the wafer 11 is covered. When the suction force (negative pressure) of the suction source is applied to the holding surface 6a in this state, the wafer 11 is held by the chuck table 6 by suction.

A protective sheet for protecting the wafer 11 may be attached to the front surface 11 a of the wafer 11 . For example, as a protective sheet, a tape including a circular film-like substrate and an adhesive layer (glue layer) provided on the substrate is used. The base material is made of resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate. Also, the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive or the like. The wafer 11 is held by the holding surface 6a of the chuck table 6 via the protective sheet.

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

In the first preparation step, a grinding wheel (first grinding wheel) 40A for processing is attached to the grinding unit 28 . The grinding wheel 40A includes an annular base (first base) 42A and a plurality of grinding wheels (first grinding wheels) 44A. The material, structure, shape, etc. of the base 42A and the grinding wheel 44A are the same as those of the base 42 and the grinding wheel 44 (see FIG. 1, etc.).

Note that each of the plurality of grinding wheels 44A contains abrasive grains (first abrasive grains). For example, diamond having an average grain size of 20 μm or more and 60 μm or less is used as the first abrasive grains. A plurality of grinding wheels 44A are arranged in a ring on the lower surface side of the base 42A.

The chuck table 6 holding the wafer 11 is moved along the X-axis direction by the 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 track of the grinding wheel 44A overlap. For example, when the grinding wheel 40A is rotated, the front end (the left end in FIG. 4(B)) of the annular trajectory drawn by the end of the grinding wheel 44A on the outer peripheral edge side of the base 42A is arranged directly above the point P. , the position of the chuck table 6 in the X-axis direction is adjusted.

Next, by bringing the grinding stone 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 central portion of the wafer 11 (preparatory grinding step). FIG. 5A is a perspective view showing the grinding device 2 in the preliminary grinding step, and FIG. 5B is a side view showing the grinding device 2 in the preliminary grinding step.

In the preliminary grinding step, the chuck table 6 and the grinding wheel 40A are relatively moved along the direction perpendicular to the holding surface 6a of the chuck table 6 (the Z-axis direction) while rotating the chuck table 6 and the grinding wheel 40A. Let Specifically, the grinding unit 28 is lowered by the moving mechanism 16 (see FIG. 1) to move the grinding wheel 44A toward the wafer 11. As shown in FIG. 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.

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. Also, the lowering speed (processing feed speed) of the grinding wheel 40A is set to, for example, 1 μm/s or more and 6 μm/s or less.

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 protrusion 11d having a radius corresponding to the distance D remains at the center of the wafer 11 .

Note that the distance D is set so as to approximately match the radius of the product wafer. For example, if the product wafer is a 6-inch (150 mm diameter) silicon wafer, the distance D is set to 75 mm. As a result, the protrusions 11d are formed that have a shape and size that are substantially the same as those of the product wafer. That is, the convex portion 11d corresponding to the product wafer is formed in the central portion of the wafer 11 by the preparatory grinding step.

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

In the second preparation step, first, the grinding unit 28 is lifted 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 the grinding wheel (second grinding wheel) 40B for evaluation is attached to the grinding unit 28. FIG. The grinding wheel 40B is a grinding wheel to be evaluated for grinding, that is, a grinding wheel that is assumed to be used for grinding product wafers.

The grinding wheel 40B includes an annular base (second base) 42B and a plurality of grinding wheels (second grinding wheels) 44B. The material, structure, shape, etc. of the base 42B and the grinding wheel 44B are the same as those of the base 42 and the grinding wheel 44 (see FIG. 1, etc.).

Note that each of the plurality of grinding wheels 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 grain size of 20 μm or more and 60 μm or less is used as the second abrasive grains. Further, when the grinding wheel 40B is a grinding wheel for finish grinding, for example, diamond having an average grain size of 0.5 μm or more and 20 μm or less is used as the second abrasive grains. A plurality of grinding wheels 44B are arranged in a ring on the lower surface side of the base 42B.

Then, in the second preparation step, the chuck table 6 and the grinding wheel are ground 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 projection 11d) and the rotation orbit of the grinding wheel 44B overlap each other. The positional relationship with the wheel 40B is adjusted. For example, when the grinding wheel 40B is rotated, the front end (the left end in FIG. 6B) of the annular locus drawn by the end of the grinding wheel 44B on the outer peripheral edge side of the base 42B is arranged directly above the center of the wafer 11. The position of the chuck table 6 in the X-axis direction is adjusted so that

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

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

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 descending speed (processing 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 grinding wheel for rough grinding, the processing feed rate is set to, for example, 1 μm/s or more and 6 μm/s or less. Moreover, when the grinding wheel 40B is a grinding wheel for finish grinding, the processing feed rate is set to, for example, 0.5 μm/s or more and 2 μm/s or less.

Grinding of the convex portion 11d by the grinding wheel 40B proceeds in the same manner as grinding a product wafer having a radius D with the grinding wheel 40B. That is, by grinding the convex portion 11d with the grinding wheel 40B, grinding of the product wafer with the grinding wheel 40B can be imagined. This makes it possible to evaluate the grinding of the product wafer by the grinding wheel 40B.

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

By adjusting the distance D in the first preparation step (see FIGS. 4A and 4B), it is possible to grind the convex portion 11d of any size in the evaluation grinding step. This makes it possible to use the wafer 11 to evaluate grinding when a product wafer of any size is ground by the grinding wheel 40B. For example, when an 8-inch silicon wafer is used as the wafer 11, the projection 11d corresponding to the 2-inch to 6-inch silicon wafer can be ground in the evaluation grinding step.

Grinding of the wafer 11 by the grinding device 2 is realized by controlling the operation of each component of the grinding device 2 with the control unit 46 (see FIG. 1). Specifically, the storage section (memory) of the control unit 46 stores the configuration of the grinding apparatus 2 necessary for sequentially performing the holding step, the first preparation step, the preparation grinding step, the second preparation step, and the evaluation grinding step. A program is stored that describes the sequence of actions of the elements. Then, when performing grinding evaluation, the control unit 46 reads out the program from the storage section, executes it, and sequentially outputs control signals to the constituent elements of the grinding apparatus 2 . As a result, the operation of the grinding device 2 is controlled, and the grinding evaluation method according to this embodiment is automatically performed.

As described above, in the grinding evaluation method according to the present embodiment, the outer peripheral portion 11c of the wafer 11 held by the chuck table 6 is ground by the grinding wheel 44A to form the convex portion 11d at the central portion of the wafer 11, and then the convex portion 11d is formed. The portion 11d is ground with a grinding wheel 44B. This makes it possible to evaluate the grinding of a product wafer of any size smaller in diameter than the wafer 11 using the chuck table 6 that matches the size of the wafer 11 . As a result, the replacement work of the chuck table 6 and the self-grinding of the holding surface 6a are omitted, and the grinding evaluation process is simplified.

In the above embodiment, the grinding wheel 40A (see FIGS. 5A and 5B) for grinding the outer peripheral portion 11c of the wafer 11 and the grinding wheel 40B for grinding the convex portion 11d of the wafer 11 (FIG. 7) are used. (A) and FIG. 7(B)) have been described. However, the grinding wheel subject to grinding evaluation can also be used for grinding the outer peripheral portion 11 c of the wafer 11 . In this case, the grinding wheel 40A and the grinding wheel 40B are the same grinding wheel, and the grinding wheel 44A and the grinding wheel 44B are the same grinding wheel. This eliminates the work of replacing the grinding wheel 40A with the grinding wheel 40B between the preparatory grinding step and the evaluation grinding step.

Alternatively, the grinding device 2 may have two sets of grinding units 28 . In this case, the preliminary grinding step is performed by one grinding unit 28 fitted with grinding wheel 40A and the evaluation grinding step is performed by the other grinding unit 28 fitted with grinding wheel 40B. Accordingly, even if the grinding wheel 40A and the grinding wheel 40B are different grinding wheels, it is unnecessary to replace the grinding wheels.

Furthermore, the wafer 11 may be processed by two grinding devices 2. FIG. In this case, the grinding wheel 40A is attached to the grinding unit 28 of one grinding device 2, and the grinding wheel 40B is attached to the grinding unit 28 of the other grinding device 2. FIG. A preparatory grinding step is then carried out by one grinding device 2 and an evaluation grinding step is carried out by the other grinding device 2 .

In addition, the structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

11 wafer 11a surface (first surface)
11b back surface (second surface)
11c outer peripheral portion 11d convex portion 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 cushioning 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 wheel 44A grinding wheel (first grinding wheel)
44B grinding wheel (second grinding wheel)
46 control unit (control unit, control device)
48 frame body (main body)
48a upper surface 48b concave portion 50 holding member 50a suction surface

Claims (2)

A grinding evaluation method for evaluating grinding of a wafer by a grinding wheel,
a holding step of holding the wafer by a chuck table including a holding surface and having a rotation axis set along a direction perpendicular to the holding surface;
after the holding step, so that a point separated by a predetermined distance from the rotation axis of the chuck table in a direction parallel to the holding surface and the rotational trajectory of the first grinding wheel included in the first grinding wheel overlap; a first preparatory step of adjusting the positional relationship between the chuck table and the first grinding wheel;
After the first preparation step, while rotating the chuck table and the first grinding wheel, the chuck table and the first grinding wheel are relatively moved in a direction perpendicular to the holding surface. A preparatory grinding step of grinding the outer peripheral portion of the wafer by bringing the first grinding wheel into contact with the outer peripheral portion of the wafer to form a protrusion having a radius corresponding to the predetermined distance in the central portion of the wafer. When,
After the preparatory grinding step, the positional relationship between the chuck table and the second grinding wheel is adjusted so that the rotation axis of the chuck table and the rotation orbit of the second grinding wheel included in the second grinding wheel overlap. a second preparatory step;
After the second preparation step, while rotating the chuck table and the second grinding wheel, the chuck table and the second grinding wheel are relatively moved in a direction perpendicular to the holding surface. and an evaluation grinding step of grinding the projection by bringing the second grinding wheel into contact with the projection. the first grinding wheel and the second grinding wheel are the same grinding wheel;
2. The grinding evaluation method according to claim 1, wherein the first grinding wheel and the second grinding wheel are the same grinding wheel.

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