JP2024053411A - Wafer grinding method and grinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grind a wafer efficiently in short time.

SOLUTION: A method of grinding a wafer 100 uses a grinder 1 which comprises: a first grinding mechanism 20 to which a first grindstone 262 is mounted; a first perpendicular movement mechanism 40 for moving the first grinding mechanism 20 in a perpendicular direction; a second grinding mechanism 30 to which a second grindstone 362 is mounted; and a second perpendicular movement mechanism 50 for moving the second grinding mechanism 30 in a perpendicular direction. The method of grinding a wafer 100 includes: a first grinding process in which the second grindstone 362 is lowered in advance of the first grindstone 262, and the wafer 100 is ground using the first grindstone 262 and the second grindstone 362 until a thickness of a ground section of the wafer 100 ground by the second grindstone 362 is a set thickness t1 being slightly thicker than a preset finished thickness t0; and a second process in which the second grindstone 362 is elevated and alienated from the wafer 100, and the wafer 100 is ground using only the first grindstone 262 until a thickness of the entire plane of the wafer becomes the finished thickness t0.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method and apparatus for grinding wafers using two grinding wheels, a first grinding wheel and a second grinding wheel.

A grinding device that grinds the surface of a wafer rotates an annular grinding wheel so that the wheel passes through the center of the wafer, and grinds the wafer with the lower surface of the grinding wheel (see, for example, Patent Document 1).
Patent Document 2 proposes a technology in which, when grinding wafers made of a hard material such as sapphire or SiC, the grinding load is reduced by inclining the grinding surface of the grinding wheel at a predetermined angle relative to the holding surface of a rotating chuck table, and then grinding is performed with the grinding surface of the grinding wheel and the holding surface of the chuck table parallel to each other.

Furthermore, in Patent Document 3, in order to grind large-diameter wafers without using large-diameter grinding wheels, the holding surface of the chuck table is formed with a first inclined surface whose apex is the center of rotation, and a second inclined surface that spreads radially from the first inclined surface and has a larger inclination angle than the first inclined surface, and the first annular grinding wheel of the first grinding means is arranged parallel to the first inclined surface, and the second annular grinding wheel of the second grinding means is arranged parallel to the second inclined surface.

JP 2008-047697 A JP 2018-020398 A JP 2014-037020 A

However, the grinding method described in Patent Document 2 has a problem in that the angle of the grinding surface of the grinding wheel is changed during grinding, which takes a long time for the grinding.
Furthermore, in the grinding apparatus described in Patent Document 3, the holding surface of the chuck table is equipped with a first inclined surface and a second inclined surface, so that, for example, it is necessary to grind the annular portion of the wafer held on the second inclined surface of the chuck table with a second grinding wheel attached to the second grinding means, and then to grind the central portion of the wafer held on the first inclined surface of the chuck table with a first grinding wheel attached to the first grinding means, which results in a problem of long grinding time and low efficiency.

Therefore, the wafer grinding method and grinding device have the challenge of grinding wafers efficiently in a short time.

A method for grinding a wafer according to the present invention is a method for grinding a wafer using a grinding device that grinds a wafer with an annular grinding wheel while rotating a wafer held on a holding surface of a chuck table around an axis of the center of the wafer, the grinding device comprising: a first grinding mechanism equipped with a first grinding wheel having an inner diameter larger than the radius of the wafer; a first vertical movement mechanism that moves the first grinding mechanism in a direction perpendicular to the holding surface; a second grinding mechanism equipped with a second grinding wheel; and a second vertical movement mechanism that moves the second grinding mechanism in a direction perpendicular to the holding surface, a first grinding step in which the second grinding wheel is lowered prior to the first grinding wheel using a second vertical movement mechanism, and the wafer is ground with the first grinding wheel and the second grinding wheel until the thickness of the annular ground portion of the wafer ground by the second grinding wheel reaches a set thickness that is slightly thicker than a preset finish thickness; and a second grinding step in which, after the first grinding step, the second grinding wheel is raised by the second vertical movement mechanism to separate it from the wafer, and the first grinding wheel is lowered by the first vertical movement mechanism to grind the entire surface of the wafer using only the first grinding wheel until the thickness of the entire surface of the wafer reaches the finish thickness.
Further, a grinding apparatus according to the present invention is a grinding apparatus for grinding wafers, comprising: a chuck table for holding a wafer on a holding surface and rotating the wafer around an axis of the center of the holding surface; a first grinding mechanism for grinding the wafer by rotating an annular first grinding wheel around an axis of the first grinding wheel which passes through the center of the wafer held on the holding surface and has an inner diameter larger than the radius of the wafer; a first vertical movement mechanism for moving the first grinding mechanism in a direction perpendicular to the holding surface; a first thickness measuring device for measuring the thickness of the wafer at the portion ground by the first grinding wheel; a second grinding mechanism for rotating an annular second grinding wheel around an axis of the center of the second grinding wheel to annularly grind an outer periphery of the wafer held on the holding surface; The wafer grinding machine includes a linear movement mechanism, a first thickness gauge that measures the thickness of the wafer at the portion ground by the second grinding wheel, and a control unit, the control unit being configured to precede grinding with the second grinding wheel with respect to grinding with the first grinding wheel so that the thickness measured by the first thickness gauge is thicker than the thickness measured by the second thickness gauge, and to perform grinding until the thickness measured by the second thickness gauge reaches a set thickness that is slightly thicker than a preset finish thickness, and a second control unit that, after grinding under the control of the first control unit, raises the second grinding wheel by the second vertical movement mechanism to separate the second grinding wheel from the wafer, and lowers the first grinding wheel by the first vertical movement mechanism, and performs grinding using only the first grinding wheel until the thickness of the entire surface of the wafer reaches the finish thickness.

In the grinding method of the present invention, in the first grinding step, the second grinding wheel is lowered before the first grinding wheel, so that the annular grinding part and the grinding part inside it are shared between the first grinding wheel and the second grinding wheel. Therefore, the contact area of each grinding wheel with the wafer can be reduced, which reduces the load on the grinding wheel and allows the grinding wheel to descend faster. Then, in the second grinding step, the entire surface of the wafer is ground to the finishing thickness using only the first grinding wheel, so that the wafer can be ground with the same thickness accuracy as in the conventional method. Therefore, the grinding time can be shortened while maintaining the thickness accuracy.
Furthermore, the grinding apparatus of the present invention makes it possible to carry out the above-mentioned grinding method.

1 is a partially cutaway perspective view showing a grinding device according to the present invention; 1 is a perspective view showing a first grinding wheel, a second grinding wheel, and a wafer held on a chuck table of a grinding apparatus according to the present invention; 2 is a cutaway side view showing a first grinding wheel, a second grinding wheel, and a wafer held on a chuck table of a grinding apparatus according to the present invention. FIG. 1A to 1C are schematic side views showing the steps of a wafer grinding method according to the present invention. FIG. 4 is a plan view showing a grinding area of a wafer by a first grindstone and a second grindstone. 13 is a plan view showing a grinding area of a wafer in an example in which the arrangement of the first grindstone and the second grindstone is changed. FIG. FIG. 13 is a plan view showing a grinding area of a wafer in another example in which the arrangement of the first grinding stone and the second grinding stone is changed.

[Grinding device]
The grinding apparatus 1 shown in FIG. 1 is an apparatus for grinding a disk-shaped wafer 100, and includes a chuck table 10 that holds the wafer 100 on an upper circular holding surface 11, a first grinding mechanism 20 and a second grinding mechanism 30 that grind the upper surface 100a of the wafer 100 held by suction on the holding surface 11 of the chuck table 10, a first vertical movement mechanism 40 and a second vertical movement mechanism 50 that move the first grinding mechanism 20 and the second grinding mechanism 30 up and down, respectively, in a direction perpendicular to the holding surface 11, a thickness gauge 60 that measures the thickness of the wafer 100, and a control unit 70 that controls the driving of the first vertical movement mechanism 40, the second vertical movement mechanism 50, etc.

The chuck table 10 is formed in a disk shape, and is configured by housing a disk-shaped porous member 13 (see FIG. 3) made of porous ceramic or the like in the center of a frame body 12. The upper surface of the porous member 13 forms a holding surface 11 that suction-holds the disk-shaped wafer 100, and the holding surface 11 is formed flush with the upper surface 120 of the frame body 12. The porous member 13 is connected to a suction source (not shown), such as a vacuum pump. The chuck table 10 is rotated around a central axis by a rotation drive mechanism (not shown), such as a motor.

The lower surface 100b of the wafer 100 is protected by a protective tape (not shown). The lower surface 100b to which the protective tape is attached is sucked and held by the holding surface 11 of the chuck table 10, and the upper surface 100a is ground by the first grinding mechanism 20 and the second grinding mechanism 30.

The grinding device 1 has a rectangular box-shaped base 2 that is long in the Y-axis direction (front-to-back direction), and inside this base 2 is a horizontal movement mechanism (not shown) for moving the chuck table 10 along the Y-axis direction (front-to-back direction).

As shown in FIG. 1, a rectangular opening 3 that is long in the Y-axis direction is formed on the top surface of the base 2, and a chuck table 10 is housed in this opening 3 so that it can move in the Y-axis direction. The periphery of the chuck table 10 in the opening 3 is covered by a rectangular plate-shaped cover 4, and the front and rear parts of the cover 4 of the opening 3 (-Y direction and +Y direction) are covered by a bellows-shaped expandable cover 5 that moves and expands together with the cover 4. Therefore, no matter where the chuck table 10 is located on the Y-axis, the opening 3 is always blocked by the expandable cover 5, preventing the intrusion of foreign matter into the base 2.

The first grinding mechanism 20 includes a spindle housing 22 fixed to the holder 21, a spindle 23 rotatably supported by the spindle housing 22, a first spindle motor 24 that rotates the spindle 23 around the axis center in the Z-axis direction, a mount 25 connected to the lower end of the spindle 23, and a first grinding wheel 26 detachably attached to the lower surface of the mount 25. As shown in FIG. 2, the first grinding wheel 26 includes a base 261 and a first grinding wheel 262 in the shape of an annular ring attached to the lower surface of the base 261. The first grinding wheel 262 is a processing tool for grinding the wafer 100, and its lower surface constitutes a grinding surface that contacts the wafer 100. As shown in FIG. 3, the inner diameter φd of the first grinding wheel 262 is set to be larger than the radius r of the wafer 100 held on the holding surface 11 of the chuck table 10 (φd>r).

As shown in FIG. 1, the second grinding mechanism 30 is arranged in parallel to the first grinding mechanism 20 in the -X direction, and its basic configuration is the same as that of the first grinding mechanism 20, and includes a spindle housing 32 fixed to a holder 31, a spindle 33 rotatably supported by the spindle housing 32, a second spindle motor 34 that rotates the spindle 33 around its axis in the Z-axis direction, a mount 35 connected to the lower end of the spindle 33, and a second grinding wheel 36 detachably attached to the lower surface of the mount 35. Here, the second grinding wheel 36 includes a base 361 and a second grinding stone 362 in the shape of an annular ring attached to the lower surface of the base 361.

As shown in FIG. 1, the first and second vertical movement mechanisms 40, 50 are each provided so as to be movable in the X-axis direction (left-right direction) by a horizontal movement mechanism 80 that is arranged on the -Y end face (front face) of a rectangular box-shaped column 6 that is erected vertically on the +Y end of the top surface of the base 2.

The horizontal movement mechanism 80 includes a pair of upper and lower guide rails 81 arranged along the X-axis direction (left and right direction) on the front surface of the column 6, a rotatable ball screw shaft 82 arranged along the X-axis direction between these guide rails 81, a reversible electric motor 83 that drives and rotates the ball screw shaft 82, and two sliders 84, 85 that can move in the X-axis direction along the guide rails 81.

Here, the sliders 84 and 85 have nut members (not shown) attached to their backs that screw into the ball screw shaft 82, allowing the first vertical movement mechanism 40 and the first grinding mechanism 20, and the second vertical movement mechanism 50 and the second grinding mechanism 30 to move along the ball screw shaft 82 in the X-axis direction. That is, when the ball screw shaft 82 is rotated forwards or backwards by the electric motor 83, the sliders 84 and 85, to which nut members (not shown) that screw into the ball screw shaft 82 are attached, move in the X-axis direction, and the first vertical movement mechanism 40 and the first grinding mechanism 20, and the second vertical movement mechanism 50 and the second grinding mechanism 30 move along the X-axis direction.

The first vertical movement mechanism 40 raises and lowers the first grinding mechanism 20 in a direction perpendicular to the holding surface 11 of the chuck table 10 (Z-axis direction), and raises and lowers a rectangular plate-shaped lift plate 41 attached to the back surface of the holder 21 in the Z-axis direction along a pair of left and right guide rails 42 together with the holder 21 and the spindle housing 22, spindle 23, first spindle motor 24, first grinding wheel 26, etc. held by the holder 21. Here, the pair of left and right guide rails 42 are arranged perpendicular to the front surface of the column 6 and parallel to each other.

A rotatable ball screw shaft 43 is disposed along the Z-axis direction between the pair of left and right guide rails 42, and the upper end of the ball screw shaft 43 is connected to a first motor 44 that can rotate forward and backward and is the driving source. Here, the first motor 44 is attached in a vertical position via a rectangular plate-shaped bracket 45 attached to the upper surface of the column 6. The lower end of the ball screw shaft 43 is rotatably supported by the column 6, and a nut member (not shown) that protrudes horizontally toward the rear (+Y direction) from the back surface of the lift plate 41 is screwed into the ball screw shaft 43.

Therefore, when the first motor 44 is driven to rotate the ball screw shaft 43 forward or backward, the lift plate 41, to which a nut member (not shown) that screws onto the ball screw shaft 43 is attached, moves up and down along the Z axis together with the first grinding mechanism 20.

The second vertical movement mechanism 50 raises and lowers the second grinding mechanism 30 in a direction perpendicular to the holding surface 11 of the chuck table 10 (Z-axis direction), and has the same basic configuration as the first vertical movement mechanism 40. That is, the second vertical movement mechanism 50 raises and lowers the lift plate 51 attached to the back surface of the holder 31 in the Z-axis direction along a pair of left and right guide rails 52 together with the holder 31 and the spindle housing 32, spindle 33, second spindle motor 34, second grinding wheel 36, etc. held by the holder 31.

A rotatable ball screw shaft 53 is vertically installed along the Z-axis direction between the pair of left and right guide rails 52, and the upper end of the ball screw shaft 53 is connected to a second motor 54 that can rotate forward and backward and serves as a drive source. Here, the second motor 54 is attached in a vertical position via a rectangular plate-shaped bracket 55 attached to the upper surface of the column 6. The lower end of the ball screw shaft 53 is rotatably supported by the column 6, and a nut member (not shown) that protrudes horizontally toward the rear (+Y direction) from the back surface of the lift plate 51 is screwed into the ball screw shaft 53.

Therefore, when the second motor 54 is driven to rotate the ball screw shaft 53 forward or backward, the lift plate 51, to which a nut member (not shown) that screws onto the ball screw shaft 53 is attached, moves up and down along the Z axis together with the second grinding mechanism 30.

As shown in FIG. 1, a thickness gauge 60 for measuring the thickness of the wafer 100 held on the holding surface 11 of the chuck table 10 is disposed on the side of the opening 3 on the top surface of the base 2. Here, this thickness gauge 60 includes a center height gauge 61 for measuring the height of the center of the wafer 100, a peripheral height gauge 62 for measuring the height of the peripheral portion on the outer periphery side of the center of the wafer 100, a holding surface height gauge 63 for measuring the height of the holding surface 11, a first thickness gauge 64 for measuring the thickness of the center of the wafer 100, and a second thickness gauge 65 for measuring the thickness of the peripheral portion of the wafer 100.

The central height measuring device 61, the outer peripheral height measuring device 62, and the holding surface height measuring device 63 are contact-type height gauges, and the central height measuring device 61 measures the height of the area of the wafer 100 ground by the first grinding wheel 262, the outer peripheral height measuring device 62 measures the height of the area of the wafer 100 ground by the second grinding wheel 362, and the holding surface height measuring device 63 measures the height of the holding surface 11 by contacting the upper surface 120 of the frame 12, which is formed flush with the holding surface 11.

The first thickness gauge 64 calculates the thickness of the central portion of the wafer 100 by taking the difference between the measurement value of the central height gauge 61 and the measurement value of the holding surface height gauge 63. The second thickness gauge 65 calculates the thickness of the peripheral portion of the wafer 100 by taking the difference between the measurement value of the peripheral height gauge 62 and the measurement value of the holding surface height gauge 63.

The control unit 70 includes a CPU (Central Processing Unit) that performs calculations according to a control program, and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). This control unit 70 controls the first spindle motor 24 of the first grinding mechanism 20, the second spindle motor 34 of the second grinding mechanism 30, the first motor 44 of the first vertical movement mechanism 40, and the second motor 54 of the second vertical movement mechanism 50, etc.

The control unit 70 includes a first control unit 71 and a second control unit 72 that perform the controls described below, which will be described in more detail later.

As shown in FIG. 1, the grinding device 1 according to the present embodiment includes a cassette 101 that stores a plurality of wafers 100 before grinding, a cassette 102 that stores the wafers 100 after grinding, a transfer mechanism 103 that transfers the wafers 100 into and out of the cassette 101, an alignment table 104 that positions the wafers 100 transferred from the cassette 101, a first transfer mechanism 105 that transfers the wafers 100 positioned on the alignment table 104 to the chuck table 10, a cleaning mechanism 90 that cleans the wafers 100 after grinding, and a second transfer mechanism 106 that removes the wafers 100 after grinding from the chuck table 10 and transfers them to the cleaning mechanism 90. The cleaning mechanism 90 includes a spinner table 91 that holds and rotates the wafers 100 after grinding, and an injection nozzle 92 that injects cleaning water or high-pressure air.

[Grinding method]
When the wafers 100 are ground, a plurality of wafers 100 to be processed are accommodated in a cassette 101. When the wafers 100 accommodated in the cassette 101 are taken out by a carry-in/out mechanism 103 and placed on an alignment table 104, the wafers 100 are aligned by the alignment table 104, and the aligned wafers 100 are placed on the holding surface 11 of the chuck table 10 by a first transport mechanism 105. When a suction source (not shown) connected to the porous member 13 of the chuck table 10 is driven from this state to evacuate the porous member 13, a negative pressure is generated in the porous member 13, and the wafers 100 are suction-held on the holding surface 11 by the negative pressure.

From the above state, the horizontal movement mechanism (not shown) is driven to move the chuck table 10 in the +Y direction, and the wafer 100 held by suction on the chuck table 10 is positioned below the first grinding wheel 26 of the first grinding mechanism 20 and the second grinding wheel 36 of the second grinding mechanism 30.

Here, the first control unit 71 and the second control unit 72 of the control unit 70 respectively control the first grinding process and the second grinding process described below.

(1) First Grinding Step In the first grinding step, the first control unit 71 of the control unit 70 drives a rotation drive mechanism (not shown) to rotate the chuck table 10 holding the wafer 100 counterclockwise at a predetermined speed as shown in Figures 2 and 3. At the same time, the control unit 70 drives the first motor 44 of the first vertical movement mechanism 40 and the second motor 54 of the second vertical movement mechanism 50 to rotate the first grinding wheel 26 and the second grinding wheel 36 counterclockwise at a predetermined speed as shown in Figures 2 and 3.

Here, although not shown, the holding surface 11 of the chuck table 10 is a conical surface, and the lower surfaces (grinding surfaces) of the first grinding wheel 262 and the second grinding wheel 362 are parallel to the conical surface. The first grinding wheel 262 contacts the first grinding part 301 shown in FIG. 5, i.e., the radial part passing through the center O of the wafer 100, and the second grinding wheel 362 contacts the second grinding part 302 shown in FIG. 5, i.e., the outer periphery of the wafer 100. Therefore, the first grinding wheel 262 can grind the entire surface of the rotating wafer 100. On the other hand, the second grinding wheel 362 can grind only the second grinding part 302 of the rotating wafer 100.

While the chuck table 10 holding the wafer 100, the first grinding wheel 262, and the second grinding wheel 362 are rotating, the first control unit 71 drives the first motor 44 of the first vertical movement mechanism 40 and the second motor 54 of the second vertical movement mechanism 50 to lower the first grinding wheel 262 and the second grinding wheel 362 in the -Z direction, as shown in FIG. 4(a).

In this first grinding process, the first control unit 71 lowers the second grinding wheel 362 before the first grinding wheel 262, that is, performs grinding feed so that the second grinding wheel 362 is positioned lower than the first grinding wheel 262. Then, as shown in FIG. 4(b), grinding proceeds while maintaining the annular region S2 ground by the second grinding wheel 362 thinner than the circular region S1 on the inner periphery side that is not in contact with the second grinding wheel 362.

Then, grinding of the wafer 100 by the first grindstone 262 and the second grindstone 362 continues until the thickness of the annular region S2 measured by the second thickness gauge 65 reaches a preset thickness that is slightly thicker than the preset finishing thickness (t0 shown in FIG. 4(d)).

As described above, in this first grinding process, the second grinding wheel 362 is lowered before the first grinding wheel 262 to grind the annular region S2 of the wafer 100 first, so that the first grinding wheel 262, which is lowered while positioned above the second grinding wheel 362, grinds only the circular region S1 without grinding the entire surface of the wafer 100. In this way, the first grinding wheel 262 and the second grinding wheel 362 share the grinding of the circular region S1 and the annular region S2, so the load on the first grinding wheel 262 and the second grinding wheel 362 is distributed. Therefore, the first vertical movement mechanism 40 and the second vertical movement mechanism 50 can increase the descent speed of the first grinding wheel 262 and the second grinding wheel 362.

(2) Second Grinding Process In the second grinding process, as shown in FIG. 4(c), when the measurement value of the thickness of the annular region S2 of the wafer 100 by the second grindstone 362 by the second thickness gauge 65 reaches a thickness t1 formed by the second grindstone 362 by a predetermined thickness thicker than the finishing thickness t0, the second control unit 72 causes the second vertical movement mechanism 50 to raise the second grindstone 362 to separate it from the wafer 100. Meanwhile, the first vertical movement mechanism 40 continues to lower the first grindstone 262, and grinding is performed only by the first grindstone 262. Here, at the start of this process, the circular region S1 is formed thicker than the annular region S2, so the first grindstone 262 contacts only the circular region S1 to perform grinding. Then, as grinding of the circular region S1 progresses, the circular region S1 and the annular region S2 eventually become flush with each other and have the same thickness. Then, the first grindstone 262 grinds both (entire surfaces) of the circular region S1 and the annular region S2, and continues grinding until the thickness of the entire wafer 100 becomes the finishing thickness t0 shown in Fig. 4(d) as shown in Fig. 4(d). Then, when the thickness of the wafer W measured by the first thickness gauge 64 becomes the finishing thickness t0, the second control unit 72 controls the first motor 44 of the first vertical movement mechanism 40 to raise the first grindstone 262 and finish grinding.

As described above, in the second grinding process, after the thickness of the annular region S2 of the wafer 100 ground by the second grinding wheel 362 in the first grinding process becomes slightly thicker than the finishing thickness t0, the entire wafer 100 is ground to the finishing thickness t0 by the first grinding wheel 262 alone, so that the amount of grinding by the first grinding wheel 262 can be reduced. Therefore, the grinding time of the wafer 100 by the first grinding wheel 262 is shortened and the load on the first grinding wheel 262 is reduced. Furthermore, in this second grinding process, the entire surface of the wafer 100 is ground by one first grinding wheel 262, so that the feed speed of the first grinding wheel 262 can be changed to the same speed as before, and grinding can be performed with the same thickness accuracy as before and the grinding time can be shortened.

In this way, the above grinding method allows for efficient grinding in a short time while ensuring the thickness accuracy of the wafer 100 after grinding.

When grinding of the wafer 100 is completed through the above first and second grinding processes, the horizontal movement mechanism shown in the figure is driven to move the chuck table 10 holding the wafer 100 in the -Y direction, and the wafer 100 is removed from the chuck table 10 by the second transport mechanism 106 and placed on the spinner table 91 of the cleaning mechanism 90 and held by suction.

In the cleaning mechanism 90, the wafer 100 held on the spinner table 91 rotates at a predetermined speed, and cleaning water or high-pressure air is sprayed from the spray nozzles 92 toward the rotating wafer 100 to clean the upper surface 100a. After cleaning is completed in this manner, the wafer 100 is removed from the spinner table 91 by the carry-in/out mechanism 103 and stored in the cassette 102.

5 shows an example in which the center of rotation of the first grindstone 262 and the center of rotation of the second grindstone 362 are located on an extension line in the X-axis direction, but the positional relationship between the first grindstone 262 and the second grindstone 362 is not limited to the example in FIG. 5. For example, as shown in FIG. 6, the first grindstone 262 and the second grindstone 362 may be arranged so that the extension line L1 of the chord of the first grinding part 303 ground by the first grindstone 262 and the extension line L2 of the chord of the second grinding part 304 ground by the second grindstone 362 are perpendicular to each other. When the extension line L1 of the chord of the first grinding part 303 and the extension line L2 of the chord of the second grinding part 304 are perpendicular to each other in this way, the transmission of the vibration of the first grindstone 262 to the second grindstone 362 can be suppressed, and the vibration of the second grindstone 362 can be suppressed.

Also, as shown in FIG. 7, the first grindstone 262 and the second grindstone 362 may be arranged so that the extension line L3 of the chord of the first grinding portion 305 ground by the first grindstone 262 and the extension line L4 of the chord of the second grinding portion 306 ground by the second grindstone 362 are parallel to each other. When the extension line L3 of the chord of the first grinding portion 305 and the extension line L4 of the chord of the second grinding portion 306 are parallel to each other in this way, the vibrations of the first grindstone 262 and the second grindstone 362 cancel each other out, so that the vibrations of both the first grindstone 262 and the second grindstone 362 are kept small.

The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings.

1: grinding device, 2: base, 3: opening of base, 4: cover, 5: expandable cover,
6: column, 10: chuck table, 11: holding surface of the chuck table,
12: frame, 120: upper surface, 13: porous member,
20: first grinding mechanism, 21: holder, 22: spindle housing,
23: spindle, 24: first spindle motor, 25: mount,
26: first grinding wheel, 261: base, 262: first grinding stone, 30: second grinding mechanism,
31: holder, 32: spindle housing, 33: spindle,
34: second spindle motor, 35: mount, 36: second grinding wheel,
361: base, 362: second grindstone, 40: first vertical movement mechanism, 41: lift plate,
42: guide rail, 43: ball screw shaft, 44: first motor, 45: bracket,
50: second vertical movement mechanism, 51: lift plate, 52: guide rail, 53: ball screw shaft,
54: second motor, 55: bracket,
60: thickness measuring instrument, 61: center height measuring instrument, 62: outer periphery height measuring instrument,
63: holding surface height measuring device, 64: first thickness measuring device, 65: second thickness measuring device, 70: control unit, 71: first control unit,
72: second control unit, 80: horizontal movement mechanism, 81: guide rail, 82: ball screw shaft,
83: electric motor, 84, 85: slider, 90: cleaning mechanism,
91: spinner table, 92: injection nozzle,
100: wafer, 100a: upper surface, 100b: lower surface, 101, 102: cassette, 103: loading/unloading mechanism, 104: alignment table,
105: first conveying mechanism, 106: second conveying mechanism, φd: inner diameter of first grinding wheel,
301: first grinding part, 302: second grinding part, 303: first grinding part,
304: second grinding part, 305: first grinding part, 306: second grinding part, L1: extension line of the chord of the first grinding part, L2: extension line of the chord of the second grinding part,
L3: extension line of the chord of the first grinding portion, L4: extension line of the chord of the second grinding portion,
L5: extension line of the chord of the first grinding portion, L6: extension line of the chord of the second grinding portion,
t0: Finished thickness of the wafer, t1: Set thickness of the wafer

Claims (2)

A method for grinding a wafer using a grinding device that grinds a wafer with an annular grinding wheel while rotating a wafer held on a holding surface of a chuck table about an axis of the center of the wafer, the method comprising the steps of:
The grinding device includes a first grinding mechanism equipped with a first grinding stone having an inner diameter larger than a radius of the wafer, a first vertical movement mechanism for moving the first grinding mechanism in a direction perpendicular to the holding surface, a second grinding mechanism equipped with a second grinding stone, and a second vertical movement mechanism for moving the second grinding mechanism in a direction perpendicular to the holding surface,
a first grinding step in which the second grinding wheel is lowered prior to the first grinding wheel by using the first vertical movement mechanism and the second vertical movement mechanism, and the wafer is ground with the first grinding wheel and the second grinding wheel until a thickness of an annular ground portion of the wafer ground by the second grinding wheel reaches a set thickness that is slightly thicker than a preset finish thickness;
a second grinding step in which, after the first grinding step, the second grinding wheel is raised by the second vertical movement mechanism to separate it from the wafer, and the first grinding wheel is lowered by the first vertical movement mechanism to grind the entire surface of the wafer only with the first grinding wheel until the thickness of the entire surface of the wafer reaches the finish thickness;
A method for grinding a wafer comprising the steps of: A grinding apparatus for grinding a wafer, comprising:
the wafer grinding device includes a chuck table for holding a wafer on a holding surface and rotating the wafer around an axis about the center of the holding surface; a first grinding mechanism for grinding the wafer by rotating a first grinding stone around an axis about the center of the first grinding stone, the first grinding stone having an inner diameter larger than the radius of the wafer and passing through the center of the wafer held on the holding surface; a first vertical movement mechanism for moving the first grinding mechanism in a direction perpendicular to the holding surface; a first thickness gauge for measuring the thickness of the wafer ground with the first grinding stone; a second grinding mechanism for rotating a second grinding stone around an axis about the center of a second grinding stone to annularly grind an outer periphery of the wafer held on the holding surface; a second vertical movement mechanism for moving the second grinding mechanism in a direction perpendicular to the holding surface; a first thickness gauge for measuring the thickness of the wafer ground with the second grinding stone; and a control unit;
the control unit causes grinding with the second grindstone to precede grinding with the first grindstone so that the thickness measured by the first thickness measuring device is greater than the thickness measured by the second thickness measuring device, and grinds until the thickness measured by the second thickness measuring device reaches a set thickness that is slightly greater than a preset finish thickness;
a second control unit that, after grinding under the control of the first control unit, raises the second grindstone by the second vertical movement mechanism to separate the second grindstone from the wafer, and lowers the first grindstone by the first vertical movement mechanism to grind the entire surface of the wafer using only the first grindstone until the thickness of the entire surface of the wafer reaches the finish thickness;
A grinding device comprising:

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